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Paradigm	Multi-paradigm: object-oriented,[1] procedural (imperative), functional, structured, reflective
Designed by	Guido van Rossum
Developer	Python Software Foundation
First appeared	20 February 1991; 32 years ago[2]
Stable release	3.11.2[3]  / 8 February 2023; 25 days ago
Preview release	3.12.0a5[4]  / 7 February 2023; 26 days ago
Typing discipline	Duck, dynamic, strong typing;[5] gradual (since 3.5, but ignored in CPython)[6]
OS	Windows, macOS, Linux/UNIX, Android[7][8] and more[9]
License	Python Software Foundation License
Filename extensions	.py, .pyi, .pyc, .pyd, .pyw, .pyz (since 3.5),[10] .pyo (prior to 3.5)[11]
Website	python.org
Major implementations
CPython, PyPy, Stackless Python, MicroPython, CircuitPython, IronPython, Jython
Dialects
Cython, RPython, Starlark[12]
Influenced by
ABC,[13] Ada,[14] ALGOL 68,[15] APL,[16] C,[17] C++,[18] CLU,[19] Dylan,[20] Haskell,[21][16] Icon,[22] Lisp,[23] Modula-3,[15][18] Perl,[24] Standard ML[16]
Influenced
Apache Groovy, Boo, Cobra, CoffeeScript,[25] D, F#, GDScript, Genie,[26] Go, JavaScript,[27][28] Julia,[29] Nim, Ring,[30] Ruby,[31] Swift[32]
Python Programming at Wikibooks

Python is a high-level, general-purpose programming language. Its design philosophy emphasizes code readability with the use of significant indentation.^[33]

Python is dynamically typed and garbage-collected. It supports multiple programming paradigms, including structured (particularly procedural), object-oriented and functional programming. It is often described as a «batteries included» language due to its comprehensive standard library.^[34][35]

Guido van Rossum began working on Python in the late 1980s as a successor to the ABC programming language and first released it in 1991 as Python 0.9.0.^[36] Python 2.0 was released in 2000. Python 3.0, released in 2008, was a major revision not completely backward-compatible with earlier versions. Python 2.7.18, released in 2020, was the last release of Python 2.^[37]

Python consistently ranks as one of the most popular programming languages.^{[38][39][40][41]}

History

Python was conceived in the late 1980s^[42] by Guido van Rossum at Centrum Wiskunde & Informatica (CWI) in the Netherlands as a successor to the ABC programming language, which was inspired by SETL,^[43] capable of exception handling and interfacing with the Amoeba operating system.^[13] Its implementation began in December 1989.^[44] Van Rossum shouldered sole responsibility for the project, as the lead developer, until 12 July 2018, when he announced his «permanent vacation» from his responsibilities as Python’s «benevolent dictator for life», a title the Python community bestowed upon him to reflect his long-term commitment as the project’s chief decision-maker.^[45] In January 2019, active Python core developers elected a five-member Steering Council to lead the project.^[46][47]

Python 2.0 was released on 16 October 2000, with many major new features such as list comprehensions, cycle-detecting garbage collection, reference counting, and Unicode support.^[48] Python 3.0, released on 3 December 2008, with many of its major features backported to Python 2.6.x^[49] and 2.7.x. Releases of Python 3 include the 2to3 utility, which automates the translation of Python 2 code to Python 3.^[50]

Python 2.7’s end-of-life was initially set for 2015, then postponed to 2020 out of concern that a large body of existing code could not easily be forward-ported to Python 3.^[51][52] No further security patches or other improvements will be released for it.^[53][54] Currently only 3.7 and later are supported. In 2021, Python 3.9.2 and 3.8.8 were expedited^[55] as all versions of Python (including 2.7^[56]) had security issues leading to possible remote code execution^[57] and web cache poisoning.^[58]

In 2022, Python 3.10.4 and 3.9.12 were expedited^[59] and 3.8.13, and 3.7.13, because of many security issues.^[60] When Python 3.9.13 was released in May 2022, it was announced that the 3.9 series (joining the older series 3.8 and 3.7) would only receive security fixes in the future.^[61] On September 7, 2022, four new releases were made due to a potential denial-of-service attack: 3.10.7, 3.9.14, 3.8.14, and 3.7.14.^[62][63]

As of November 2022, Python 3.11.0 is the current stable release. Notable changes from 3.10 include increased program execution speed and improved error reporting.^[64]

Design philosophy and features

Python is a multi-paradigm programming language. Object-oriented programming and structured programming are fully supported, and many of their features support functional programming and aspect-oriented programming (including metaprogramming^[65] and metaobjects).^[66] Many other paradigms are supported via extensions, including design by contract^[67][68] and logic programming.^[69]

Python uses dynamic typing and a combination of reference counting and a cycle-detecting garbage collector for memory management.^[70] It uses dynamic name resolution (late binding), which binds method and variable names during program execution.

Its design offers some support for functional programming in the Lisp tradition. It has filter,mapandreduce functions; list comprehensions, dictionaries, sets, and generator expressions.^[71] The standard library has two modules (itertools and functools) that implement functional tools borrowed from Haskell and Standard ML.^[72]

Its core philosophy is summarized in the document The Zen of Python (PEP 20), which includes aphorisms such as:^[73]

• Beautiful is better than ugly.
• Explicit is better than implicit.
• Simple is better than complex.
• Complex is better than complicated.
• Readability counts.

Rather than building all of its functionality into its core, Python was designed to be highly extensible via modules. This compact modularity has made it particularly popular as a means of adding programmable interfaces to existing applications. Van Rossum’s vision of a small core language with a large standard library and easily extensible interpreter stemmed from his frustrations with ABC, which espoused the opposite approach.^[42]

Python strives for a simpler, less-cluttered syntax and grammar while giving developers a choice in their coding methodology. In contrast to Perl’s «there is more than one way to do it» motto, Python embraces a «there should be one—and preferably only one—obvious way to do it» philosophy.^[73] Alex Martelli, a Fellow at the Python Software Foundation and Python book author, wrote: «To describe something as ‘clever’ is not considered a compliment in the Python culture.»^[74]

Python’s developers strive to avoid premature optimization and reject patches to non-critical parts of the CPython reference implementation that would offer marginal increases in speed at the cost of clarity.^[75] When speed is important, a Python programmer can move time-critical functions to extension modules written in languages such as C; or use PyPy, a just-in-time compiler. Cython is also available, which translates a Python script into C and makes direct C-level API calls into the Python interpreter.

Python’s developers aim for it to be fun to use. This is reflected in its name—a tribute to the British comedy group Monty Python^[76]—and in occasionally playful approaches to tutorials and reference materials, such as the use of the terms «spam» and «eggs» (a reference to a Monty Python sketch) in examples, instead of the often-used «foo» and «bar».^[77][78]

A common neologism in the Python community is pythonic, which has a wide range of meanings related to program style. «Pythonic» code may use Python idioms well, be natural or show fluency in the language, or conform with Python’s minimalist philosophy and emphasis on readability. Code that is difficult to understand or reads like a rough transcription from another programming language is called unpythonic.^[79][80]

Syntax and semantics

Python is meant to be an easily readable language. Its formatting is visually uncluttered and often uses English keywords where other languages use punctuation. Unlike many other languages, it does not use curly brackets to delimit blocks, and semicolons after statements are allowed but rarely used. It has fewer syntactic exceptions and special cases than C or Pascal.^[81]

Indentation

Python uses whitespace indentation, rather than curly brackets or keywords, to delimit blocks. An increase in indentation comes after certain statements; a decrease in indentation signifies the end of the current block.^[82] Thus, the program’s visual structure accurately represents its semantic structure.^[83] This feature is sometimes termed the off-side rule. Some other languages use indentation this way; but in most, indentation has no semantic meaning. The recommended indent size is four spaces.^[84]

Statements and control flow

Python’s statements include:

• The assignment statement, using a single equals sign =
• The if statement, which conditionally executes a block of code, along with else and elif (a contraction of else-if)
• The for statement, which iterates over an iterable object, capturing each element to a local variable for use by the attached block
• The while statement, which executes a block of code as long as its condition is true
• The try statement, which allows exceptions raised in its attached code block to be caught and handled by except clauses (or new syntax except* in Python 3.11 for exception groups^[85]); it also ensures that clean-up code in a finally block is always run regardless of how the block exits
• The raise statement, used to raise a specified exception or re-raise a caught exception
• The class statement, which executes a block of code and attaches its local namespace to a class, for use in object-oriented programming
• The def statement, which defines a function or method
• The with statement, which encloses a code block within a context manager (for example, acquiring a lock before it is run, then releasing the lock; or opening and closing a file), allowing resource-acquisition-is-initialization (RAII)-like behavior and replacing a common try/finally idiom^[86]
• The break statement, which exits a loop
• The continue statement, which skips the rest of the current iteration and continues with the next
• The del statement, which removes a variable—deleting the reference from the name to the value, and producing an error if the variable is referred to before it is redefined
• The pass statement, serving as a NOP, syntactically needed to create an empty code block
• The assert statement, used in debugging to check for conditions that should apply
• The yield statement, which returns a value from a generator function (and also an operator); used to implement coroutines
• The return statement, used to return a value from a function
• The import and from statements, used to import modules whose functions or variables can be used in the current program

The assignment statement (=) binds a name as a reference to a separate, dynamically allocated object. Variables may subsequently be rebound at any time to any object. In Python, a variable name is a generic reference holder without a fixed data type; however, it always refers to some object with a type. This is called dynamic typing—in contrast to statically-typed languages, where each variable may contain only a value of a certain type.

Python does not support tail call optimization or first-class continuations, and, according to Van Rossum, it never will.^[87][88] However, better support for coroutine-like functionality is provided by extending Python’s generators.^[89] Before 2.5, generators were lazy iterators; data was passed unidirectionally out of the generator. From Python 2.5 on, it is possible to pass data back into a generator function; and from version 3.3, it can be passed through multiple stack levels.^[90]

Expressions

Python’s expressions include:

• The +, -, and * operators for mathematical addition, subtraction, and multiplication are similar to other languages, but the behavior of division differs. There are two types of divisions in Python: floor division (or integer division) // and floating-point/division.^[91] Python uses the ** operator for exponentiation.
• Python uses the + operator for string concatenation. Python uses the * operator for duplicating a string a specified number of times.
• The @ infix operator. It is intended to be used by libraries such as NumPy for matrix multiplication.^[92][93]
• The syntax :=, called the «walrus operator», was introduced in Python 3.8. It assigns values to variables as part of a larger expression.^[94]
• In Python, == compares by value. Python’s is operator may be used to compare object identities (comparison by reference), and comparisons may be chained—for example, a <= b <= c.
• Python uses and, or, and not as boolean operators.
• Python has a type of expression called a list comprehension, as well as a more general expression called a generator expression.^[71]
• Anonymous functions are implemented using lambda expressions; however, there may be only one expression in each body.
• Conditional expressions are written as x if c else y^[95] (different in order of operands from the c ? x : y operator common to many other languages).
• Python makes a distinction between lists and tuples. Lists are written as [1, 2, 3], are mutable, and cannot be used as the keys of dictionaries (dictionary keys must be immutable in Python). Tuples, written as (1, 2, 3), are immutable and thus can be used as keys of dictionaries, provided all of the tuple’s elements are immutable. The + operator can be used to concatenate two tuples, which does not directly modify their contents, but produces a new tuple containing the elements of both. Thus, given the variable t initially equal to (1, 2, 3), executing t = t + (4, 5) first evaluates t + (4, 5), which yields (1, 2, 3, 4, 5), which is then assigned back to t—thereby effectively «modifying the contents» of t while conforming to the immutable nature of tuple objects. Parentheses are optional for tuples in unambiguous contexts.^[96]
• Python features sequence unpacking where multiple expressions, each evaluating to anything that can be assigned (to a variable, writable property, etc.) are associated in an identical manner to that forming tuple literals—and, as a whole, are put on the left-hand side of the equal sign in an assignment statement. The statement expects an iterable object on the right-hand side of the equal sign that produces the same number of values as the provided writable expressions; when iterated through them, it assigns each of the produced values to the corresponding expression on the left.^[97]
• Python has a «string format» operator % that functions analogously to printf format strings in C—e.g. "spam=%s eggs=%d" % ("blah", 2) evaluates to "spam=blah eggs=2". In Python 2.6+ and 3+, this was supplemented by the format() method of the str class, e.g. "spam={0} eggs={1}".format("blah", 2). Python 3.6 added «f-strings»: spam = "blah"; eggs = 2; f'spam={spam} eggs={eggs}'.^[98]
• Strings in Python can be concatenated by «adding» them (with the same operator as for adding integers and floats), e.g. "spam" + "eggs" returns "spameggs". If strings contain numbers, they are added as strings rather than integers, e.g. "2" + "2" returns "22".
• Python has various string literals:
  • Delimited by single or double quote marks; unlike in Unix shells, Perl, and Perl-influenced languages, single and double quote marks work the same. Both use the backslash () as an escape character. String interpolation became available in Python 3.6 as «formatted string literals».^[98]
  • Triple-quoted (beginning and ending with three single or double quote marks), which may span multiple lines and function like here documents in shells, Perl, and Ruby.
  • Raw string varieties, denoted by prefixing the string literal with r. Escape sequences are not interpreted; hence raw strings are useful where literal backslashes are common, such as regular expressions and Windows-style paths. (Compare «@-quoting» in C#.)
• Python has array index and array slicing expressions in lists, denoted as a[key], a[start:stop] or a[start:stop:step]. Indexes are zero-based, and negative indexes are relative to the end. Slices take elements from the start index up to, but not including, the stop index. The third slice parameter called step or stride, allows elements to be skipped and reversed. Slice indexes may be omitted—for example, a[:] returns a copy of the entire list. Each element of a slice is a shallow copy.

In Python, a distinction between expressions and statements is rigidly enforced, in contrast to languages such as Common Lisp, Scheme, or Ruby. This leads to duplicating some functionality. For example:

• List comprehensions vs. for-loops
• Conditional expressions vs. if blocks
• The eval() vs. exec() built-in functions (in Python 2, exec is a statement); the former is for expressions, the latter is for statements

Statements cannot be a part of an expression—so list and other comprehensions or lambda expressions, all being expressions, cannot contain statements. A particular case is that an assignment statement such as a = 1 cannot form part of the conditional expression of a conditional statement. This has the advantage of avoiding a classic C error of mistaking an assignment operator = for an equality operator == in conditions: if (c = 1) { ... } is syntactically valid (but probably unintended) C code, but if c = 1: ... causes a syntax error in Python.

Methods

Methods on objects are functions attached to the object’s class; the syntax instance.method(argument) is, for normal methods and functions, syntactic sugar for Class.method(instance, argument). Python methods have an explicit self parameter to access instance data, in contrast to the implicit self (or this) in some other object-oriented programming languages (e.g., C++, Java, Objective-C, Ruby).^[99] Python also provides methods, often called dunder methods (due to their names beginning and ending with double-underscores), to allow user-defined classes to modify how they are handled by native operations including length, comparison, in arithmetic operations and type conversion.^[100]

Typing

Python uses duck typing and has typed objects but untyped variable names. Type constraints are not checked at compile time; rather, operations on an object may fail, signifying that it is not of a suitable type. Despite being dynamically typed, Python is strongly typed, forbidding operations that are not well-defined (for example, adding a number to a string) rather than silently attempting to make sense of them.

Python allows programmers to define their own types using classes, most often used for object-oriented programming. New instances of classes are constructed by calling the class (for example, SpamClass() or EggsClass()), and the classes are instances of the metaclass type (itself an instance of itself), allowing metaprogramming and reflection.

Before version 3.0, Python had two kinds of classes (both using the same syntax): old-style and new-style,^[101] current Python versions only support the semantics new style.

Python supports gradual typing.^[102] Python’s syntax allows specifying static types, but they are not checked in the default implementation, CPython. An experimental optional static type-checker, mypy, supports compile-time type checking.^[103]

"""Spanning
multiple
lines"""

Spanning
multiple
lines

Arithmetic operations

Python has the usual symbols for arithmetic operators (+, -, *, /), the floor division operator // and the modulo operation % (where the remainder can be negative, e.g. 4 % -3 == -2). It also has ** for exponentiation, e.g. 5**3 == 125 and 9**0.5 == 3.0, and a matrix‑multiplication operator @ .^[107] These operators work like in traditional math; with the same precedence rules, the operators infix (+ and - can also be unary to represent positive and negative numbers respectively).

The division between integers produces floating-point results. The behavior of division has changed significantly over time:^[108]

• Current Python (i.e. since 3.0) changed / to always be floating-point division, e.g. 5/2 == 2.5.
• The floor division // operator was introduced. So 7//3 == 2, -7//3 == -3, 7.5//3 == 2.0 and -7.5//3 == -3.0. Adding from __future__ import division causes a module used in Python 2.7 to use Python 3.0 rules for division (see above).

In Python terms, / is true division (or simply division), and // is floor division. / before version 3.0 is classic division.^[108]

Rounding towards negative infinity, though different from most languages, adds consistency. For instance, it means that the equation (a + b)//b == a//b + 1 is always true. It also means that the equation b*(a//b) + a%b == a is valid for both positive and negative values of a. However, maintaining the validity of this equation means that while the result of a%b is, as expected, in the half-open interval [0, b), where b is a positive integer, it has to lie in the interval (b, 0] when b is negative.^[109]

Python provides a round function for rounding a float to the nearest integer. For tie-breaking, Python 3 uses round to even: round(1.5) and round(2.5) both produce 2.^[110] Versions before 3 used round-away-from-zero: round(0.5) is 1.0, round(-0.5) is −1.0.^[111]

Python allows boolean expressions with multiple equality relations in a manner that is consistent with general use in mathematics. For example, the expression a < b < c tests whether a is less than b and b is less than c.^[112] C-derived languages interpret this expression differently: in C, the expression would first evaluate a < b, resulting in 0 or 1, and that result would then be compared with c.^[113]

Python uses arbitrary-precision arithmetic for all integer operations. The Decimal type/class in the decimal module provides decimal floating-point numbers to a pre-defined arbitrary precision and several rounding modes.^[114] The Fraction class in the fractions module provides arbitrary precision for rational numbers.^[115]

Due to Python’s extensive mathematics library, and the third-party library NumPy that further extends the native capabilities, it is frequently used as a scientific scripting language to aid in problems such as numerical data processing and manipulation.^[116][117]

Programming examples

Hello world program:

Program to calculate the factorial of a positive integer:

n = int(input('Type a number, and its factorial will be printed: '))

if n < 0:
    raise ValueError('You must enter a non-negative integer')

factorial = 1
for i in range(2, n + 1):
    factorial *= i

print(factorial)

Libraries

Python’s large standard library^[118] provides tools suited to many tasks and is commonly cited as one of its greatest strengths. For Internet-facing applications, many standard formats and protocols such as MIME and HTTP are supported. It includes modules for creating graphical user interfaces, connecting to relational databases, generating pseudorandom numbers, arithmetic with arbitrary-precision decimals,^[119] manipulating regular expressions, and unit testing.

Some parts of the standard library are covered by specifications—for example, the Web Server Gateway Interface (WSGI) implementation wsgiref follows PEP 333^[120]—but most are specified by their code, internal documentation, and test suites. However, because most of the standard library is cross-platform Python code, only a few modules need altering or rewriting for variant implementations.

As of 14 November 2022, the Python Package Index (PyPI), the official repository for third-party Python software, contains over 415,000^[121] packages with a wide range of functionality, including:

Development environments

Most Python implementations (including CPython) include a read–eval–print loop (REPL), permitting them to function as a command line interpreter for which users enter statements sequentially and receive results immediately.

Python also comes with an Integrated development environment (IDE) called IDLE, which is more beginner-oriented.

Other shells, including IDLE and IPython, add further abilities such as improved auto-completion, session state retention, and syntax highlighting.

As well as standard desktop integrated development environments, there are Web browser-based IDEs, including SageMath, for developing science- and math-related programs; PythonAnywhere, a browser-based IDE and hosting environment; and Canopy IDE, a commercial IDE emphasizing scientific computing.^[122]

Implementations

Reference implementation

CPython is the reference implementation of Python. It is written in C, meeting the C89 standard (Python 3.11 uses C11^[123]) with several select C99 features (With later C versions out, it is considered outdated.^[124][125] CPython includes its own C extensions, but third-party extensions are not limited to older C versions—e.g. they can be implemented with C11 or C++.^[126][127]) It compiles Python programs into an intermediate bytecode^[128] which is then executed by its virtual machine.^[129] CPython is distributed with a large standard library written in a mixture of C and native Python, and is available for many platforms, including Windows (starting with Python 3.9, the Python installer deliberately fails to install on Windows 7 and 8;^[130][131] Windows XP was supported until Python 3.5) and most modern Unix-like systems, including macOS (and Apple M1 Macs, since Python 3.9.1, with experimental installer) and unofficial support for e.g. VMS.^[132] Platform portability was one of its earliest priorities.^[133] (During Python 1 and 2 development, even OS/2 and Solaris were supported,^[134] but support has since been dropped for many platforms.)

Other implementations

• PyPy is a fast, compliant interpreter of Python 2.7 and 3.8.^[135][136] Its just-in-time compiler often brings a significant speed improvement over CPython but some libraries written in C cannot be used with it.^[137]
• Stackless Python is a significant fork of CPython that implements microthreads; it does not use the call stack in the same way, thus allowing massively concurrent programs. PyPy also has a stackless version.^[138]
• MicroPython and CircuitPython are Python 3 variants optimized for microcontrollers, including Lego Mindstorms EV3.^[139]
• Pyston is a variant of the Python runtime that uses just-in-time compilation to speed up the execution of Python programs.^[140]
• Cinder is a performance-oriented fork of CPython 3.8 that contains a number of optimizations including bytecode inline caching, eager evaluation of coroutines, a method-at-a-time JIT, and an experimental bytecode compiler.^[141]

Unsupported implementations

Other just-in-time Python compilers have been developed, but are now unsupported:

• Google began a project named Unladen Swallow in 2009, with the aim of speeding up the Python interpreter fivefold by using the LLVM, and of improving its multithreading ability to scale to thousands of cores,^[142] while ordinary implementations suffer from the global interpreter lock.
• Psyco is a discontinued just-in-time specializing compiler that integrates with CPython and transforms bytecode to machine code at runtime. The emitted code is specialized for certain data types and is faster than the standard Python code. Psyco does not support Python 2.7 or later.
• PyS60 was a Python 2 interpreter for Series 60 mobile phones released by Nokia in 2005. It implemented many of the modules from the standard library and some additional modules for integrating with the Symbian operating system. The Nokia N900 also supports Python with GTK widget libraries, enabling programs to be written and run on the target device.^[143]

Cross-compilers to other languages

There are several compilers to high-level object languages, with either unrestricted Python, a restricted subset of Python, or a language similar to Python as the source language:

• Brython,^[144] Transcrypt^[145][146] and Pyjs (latest release in 2012) compile Python to JavaScript.
• Cython compiles (a superset of) Python to C (while the resulting code is also usable with Python and also e.g. C++).
• Nuitka compiles Python into C.^[147]
• Numba uses LLVM to compile a subset of Python to machine code.
• Pythran compiles a subset of Python 3 to C++ (C++11).^{[148][149][150]}
• RPython can be compiled to C, and is used to build the PyPy interpreter of Python.
• The Python → 11l → C++ transpiler^[151] compiles a subset of Python 3 to C++ (C++17).

Specialized:

• MyHDL is a Python-based hardware description language (HDL), that converts MyHDL code to Verilog or VHDL code.

Older projects (or not to be used with Python 3.x and latest syntax):

• Google’s Grumpy (latest release in 2017) transpiles Python 2 to Go.^{[152][153][154]}
• IronPython allows running Python 2.7 programs (and an alpha, released in 2021, is also available for «Python 3.4, although features and behaviors from later versions may be included»^[155]) on the .NET Common Language Runtime.^[156]
• Jython compiles Python 2.7 to Java bytecode, allowing the use of the Java libraries from a Python program.^[157]
• Pyrex (latest release in 2010) and Shed Skin (latest release in 2013) compile to C and C++ respectively.

Performance

Performance comparison of various Python implementations on a non-numerical (combinatorial) workload was presented at EuroSciPy ’13.^[158] Python’s performance compared to other programming languages is also benchmarked by The Computer Language Benchmarks Game.^[159]

Development

Python’s development is conducted largely through the Python Enhancement Proposal (PEP) process, the primary mechanism for proposing major new features, collecting community input on issues, and documenting Python design decisions.^[160] Python coding style is covered in PEP 8.^[161] Outstanding PEPs are reviewed and commented on by the Python community and the steering council.^[160]

Enhancement of the language corresponds with the development of the CPython reference implementation. The mailing list python-dev is the primary forum for the language’s development. Specific issues were originally discussed in the Roundup bug tracker hosted at by the foundation.^[162] In 2022, all issues and discussions were migrated to GitHub.^[163] Development originally took place on a self-hosted source-code repository running Mercurial, until Python moved to GitHub in January 2017.^[164]

CPython’s public releases come in three types, distinguished by which part of the version number is incremented:

• Backward-incompatible versions, where code is expected to break and needs to be manually ported. The first part of the version number is incremented. These releases happen infrequently—version 3.0 was released 8 years after 2.0. According to Guido van Rossum, a version 4.0 is very unlikely to ever happen.^[165]
• Major or «feature» releases are largely compatible with the previous version but introduce new features. The second part of the version number is incremented. Starting with Python 3.9, these releases are expected to happen annually.^[166][167] Each major version is supported by bug fixes for several years after its release.^[168]
• Bugfix releases,^[169] which introduce no new features, occur about every 3 months and are made when a sufficient number of bugs have been fixed upstream since the last release. Security vulnerabilities are also patched in these releases. The third and final part of the version number is incremented.^[169]

Many alpha, beta, and release-candidates are also released as previews and for testing before final releases. Although there is a rough schedule for each release, they are often delayed if the code is not ready. Python’s development team monitors the state of the code by running the large unit test suite during development.^[170]

The major academic conference on Python is PyCon. There are also special Python mentoring programs, such as Pyladies.

Python 3.10 deprecated wstr (to be removed in Python 3.12; meaning Python extensions^[171] need to be modified by then),^[172] and added pattern matching to the language.^[173]

API documentation generators

Tools that can generate documentation for Python API include pydoc (available as part of the standard library), Sphinx, Pdoc and its forks, Doxygen and Graphviz, among others.^[174]

Naming

Python’s name is derived from the British comedy group Monty Python, whom Python creator Guido van Rossum enjoyed while developing the language. Monty Python references appear frequently in Python code and culture;^[175] for example, the metasyntactic variables often used in Python literature are spam and eggs instead of the traditional foo and bar.^[175][176] The official Python documentation also contains various references to Monty Python routines.^[177][178]

The prefix Py- is used to show that something is related to Python. Examples of the use of this prefix in names of Python applications or libraries include Pygame, a binding of SDL to Python (commonly used to create games); PyQt and PyGTK, which bind Qt and GTK to Python respectively; and PyPy, a Python implementation originally written in Python.

Popularity

Since 2003, Python has consistently ranked in the top ten most popular programming languages in the TIOBE Programming Community Index where as of December 2022 it was the most popular language (ahead of C, C++, and Java).^[40] It was selected Programming Language of the Year (for «the highest rise in ratings in a year») in 2007, 2010, 2018, and 2020 (the only language to have done so four times as of 2020^[179]).

An empirical study found that scripting languages, such as Python, are more productive than conventional languages, such as C and Java, for programming problems involving string manipulation and search in a dictionary, and determined that memory consumption was often «better than Java and not much worse than C or C++».^[180]

Large organizations that use Python include Wikipedia, Google,^[181] Yahoo!,^[182] CERN,^[183] NASA,^[184] Facebook,^[185] Amazon, Instagram,^[186] Spotify,^[187] and some smaller entities like ILM^[188] and ITA.^[189] The social news networking site Reddit was written mostly in Python.^[190]

Uses

Python can serve as a scripting language for web applications, e.g., via mod_wsgi for the Apache webserver.^[191] With Web Server Gateway Interface, a standard API has evolved to facilitate these applications. Web frameworks like Django, Pylons, Pyramid, TurboGears, web2py, Tornado, Flask, Bottle, and Zope support developers in the design and maintenance of complex applications. Pyjs and IronPython can be used to develop the client-side of Ajax-based applications. SQLAlchemy can be used as a data mapper to a relational database. Twisted is a framework to program communications between computers, and is used (for example) by Dropbox.

Libraries such as NumPy, SciPy, and Matplotlib allow the effective use of Python in scientific computing,^[192][193] with specialized libraries such as Biopython and Astropy providing domain-specific functionality. SageMath is a computer algebra system with a notebook interface programmable in Python: its library covers many aspects of mathematics, including algebra, combinatorics, numerical mathematics, number theory, and calculus.^[194] OpenCV has Python bindings with a rich set of features for computer vision and image processing.^[195]

Python is commonly used in artificial intelligence projects and machine learning projects with the help of libraries like TensorFlow, Keras, Pytorch, and scikit-learn.^{[196][197][198][199]} As a scripting language with a modular architecture, simple syntax, and rich text processing tools, Python is often used for natural language processing.^[200]

Python can also be used to create games, with libraries such as Pygame, which can make 2D games.

Python has been successfully embedded in many software products as a scripting language, including in finite element method software such as Abaqus, 3D parametric modelers like FreeCAD, 3D animation packages such as 3ds Max, Blender, Cinema 4D, Lightwave, Houdini, Maya, modo, MotionBuilder, Softimage, the visual effects compositor Nuke, 2D imaging programs like GIMP,^[201] Inkscape, Scribus and Paint Shop Pro,^[202] and musical notation programs like scorewriter and capella. GNU Debugger uses Python as a pretty printer to show complex structures such as C++ containers. Esri promotes Python as the best choice for writing scripts in ArcGIS.^[203] It has also been used in several video games,^[204][205] and has been adopted as first of the three available programming languages in Google App Engine, the other two being Java and Go.^[206]

Many operating systems include Python as a standard component. It ships with most Linux distributions,^[207] AmigaOS 4 (using Python 2.7), FreeBSD (as a package), NetBSD, and OpenBSD (as a package) and can be used from the command line (terminal). Many Linux distributions use installers written in Python: Ubuntu uses the Ubiquity installer, while Red Hat Linux and Fedora Linux use the Anaconda installer. Gentoo Linux uses Python in its package management system, Portage.

Python is used extensively in the information security industry, including in exploit development.^[208][209]

Most of the Sugar software for the One Laptop per Child XO, developed at Sugar Labs since 2008, is written in Python.^[210] The Raspberry Pi single-board computer project has adopted Python as its main user-programming language.

LibreOffice includes Python and intends to replace Java with Python. Its Python Scripting Provider is a core feature^[211] since Version 4.0 from 7 February 2013.

Languages influenced by Python

Python’s design and philosophy have influenced many other programming languages:

• Boo uses indentation, a similar syntax, and a similar object model.^[212]
• Cobra uses indentation and a similar syntax, and its Acknowledgements document lists Python first among languages that influenced it.^[213]
• CoffeeScript, a programming language that cross-compiles to JavaScript, has Python-inspired syntax.
• ECMAScript/JavaScript borrowed iterators and generators from Python.^[214]
• GDScript, a scripting language very similar to Python, built-in to the Godot game engine.^[215]
• Go is designed for the «speed of working in a dynamic language like Python»^[216] and shares the same syntax for slicing arrays.
• Groovy was motivated by the desire to bring the Python design philosophy to Java.^[217]
• Julia was designed to be «as usable for general programming as Python».^[29]
• Nim uses indentation and similar syntax.^[218]
• Ruby’s creator, Yukihiro Matsumoto, has said: «I wanted a scripting language that was more powerful than Perl, and more object-oriented than Python. That’s why I decided to design my own language.»^[219]
• Swift, a programming language developed by Apple, has some Python-inspired syntax.^[220]

Python’s development practices have also been emulated by other languages. For example, the practice of requiring a document describing the rationale for, and issues surrounding, a change to the language (in Python, a PEP) is also used in Tcl,^[221] Erlang,^[222] and Swift.^[223]

See also

• Python syntax and semantics
• pip (package manager)
• List of programming languages
• History of programming languages
• Comparison of programming languages

References

Sources

• «Python for Artificial Intelligence». Wiki.python.org. 19 July 2012. Archived from the original on 1 November 2012. Retrieved 3 December 2012.
• Paine, Jocelyn, ed. (August 2005). «AI in Python». AI Expert Newsletter. Amzi!. Archived from the original on 26 March 2012. Retrieved 11 February 2012.
• «PyAIML 0.8.5 : Python Package Index». Pypi.python.org. Retrieved 17 July 2013.
• Russell, Stuart J. & Norvig, Peter (2009). Artificial Intelligence: A Modern Approach (3rd ed.). Upper Saddle River, NJ: Prentice Hall. ISBN 978-0-13-604259-4.

Further reading

• Downey, Allen B. (May 2012). Think Python: How to Think Like a Computer Scientist (version 1.6.6 ed.). ISBN 978-0-521-72596-5.
• Hamilton, Naomi (5 August 2008). «The A-Z of Programming Languages: Python». Computerworld. Archived from the original on 29 December 2008. Retrieved 31 March 2010.
• Lutz, Mark (2013). Learning Python (5th ed.). O’Reilly Media. ISBN 978-0-596-15806-4.
• Summerfield, Mark (2009). Programming in Python 3 (2nd ed.). Addison-Wesley Professional. ISBN 978-0-321-68056-3.
• Ramalho, Luciano (May 2022). Fluent Python (2nd ed.). O’Reilly Media. ISBN 978-1-4920-5632-4.

External links

• Official website

Paradigm	Multi-paradigm: object-oriented,[1] procedural (imperative), functional, structured, reflective
Designed by	Guido van Rossum
Developer	Python Software Foundation
First appeared	20 February 1991; 32 years ago[2]
Stable release	3.11.2[3]  / 8 February 2023; 25 days ago
Preview release	3.12.0a5[4]  / 7 February 2023; 26 days ago
Typing discipline	Duck, dynamic, strong typing;[5] gradual (since 3.5, but ignored in CPython)[6]
OS	Windows, macOS, Linux/UNIX, Android[7][8] and more[9]
License	Python Software Foundation License
Filename extensions	.py, .pyi, .pyc, .pyd, .pyw, .pyz (since 3.5),[10] .pyo (prior to 3.5)[11]
Website	python.org
Major implementations
CPython, PyPy, Stackless Python, MicroPython, CircuitPython, IronPython, Jython
Dialects
Cython, RPython, Starlark[12]
Influenced by
ABC,[13] Ada,[14] ALGOL 68,[15] APL,[16] C,[17] C++,[18] CLU,[19] Dylan,[20] Haskell,[21][16] Icon,[22] Lisp,[23] Modula-3,[15][18] Perl,[24] Standard ML[16]
Influenced
Apache Groovy, Boo, Cobra, CoffeeScript,[25] D, F#, GDScript, Genie,[26] Go, JavaScript,[27][28] Julia,[29] Nim, Ring,[30] Ruby,[31] Swift[32]
Python Programming at Wikibooks

Python is a high-level, general-purpose programming language. Its design philosophy emphasizes code readability with the use of significant indentation.^[33]

Python is dynamically typed and garbage-collected. It supports multiple programming paradigms, including structured (particularly procedural), object-oriented and functional programming. It is often described as a «batteries included» language due to its comprehensive standard library.^[34][35]

Guido van Rossum began working on Python in the late 1980s as a successor to the ABC programming language and first released it in 1991 as Python 0.9.0.^[36] Python 2.0 was released in 2000. Python 3.0, released in 2008, was a major revision not completely backward-compatible with earlier versions. Python 2.7.18, released in 2020, was the last release of Python 2.^[37]

Python consistently ranks as one of the most popular programming languages.^{[38][39][40][41]}

History

Python was conceived in the late 1980s^[42] by Guido van Rossum at Centrum Wiskunde & Informatica (CWI) in the Netherlands as a successor to the ABC programming language, which was inspired by SETL,^[43] capable of exception handling and interfacing with the Amoeba operating system.^[13] Its implementation began in December 1989.^[44] Van Rossum shouldered sole responsibility for the project, as the lead developer, until 12 July 2018, when he announced his «permanent vacation» from his responsibilities as Python’s «benevolent dictator for life», a title the Python community bestowed upon him to reflect his long-term commitment as the project’s chief decision-maker.^[45] In January 2019, active Python core developers elected a five-member Steering Council to lead the project.^[46][47]

Python 2.0 was released on 16 October 2000, with many major new features such as list comprehensions, cycle-detecting garbage collection, reference counting, and Unicode support.^[48] Python 3.0, released on 3 December 2008, with many of its major features backported to Python 2.6.x^[49] and 2.7.x. Releases of Python 3 include the 2to3 utility, which automates the translation of Python 2 code to Python 3.^[50]

Python 2.7’s end-of-life was initially set for 2015, then postponed to 2020 out of concern that a large body of existing code could not easily be forward-ported to Python 3.^[51][52] No further security patches or other improvements will be released for it.^[53][54] Currently only 3.7 and later are supported. In 2021, Python 3.9.2 and 3.8.8 were expedited^[55] as all versions of Python (including 2.7^[56]) had security issues leading to possible remote code execution^[57] and web cache poisoning.^[58]

In 2022, Python 3.10.4 and 3.9.12 were expedited^[59] and 3.8.13, and 3.7.13, because of many security issues.^[60] When Python 3.9.13 was released in May 2022, it was announced that the 3.9 series (joining the older series 3.8 and 3.7) would only receive security fixes in the future.^[61] On September 7, 2022, four new releases were made due to a potential denial-of-service attack: 3.10.7, 3.9.14, 3.8.14, and 3.7.14.^[62][63]

As of November 2022, Python 3.11.0 is the current stable release. Notable changes from 3.10 include increased program execution speed and improved error reporting.^[64]

Design philosophy and features

Python is a multi-paradigm programming language. Object-oriented programming and structured programming are fully supported, and many of their features support functional programming and aspect-oriented programming (including metaprogramming^[65] and metaobjects).^[66] Many other paradigms are supported via extensions, including design by contract^[67][68] and logic programming.^[69]

Python uses dynamic typing and a combination of reference counting and a cycle-detecting garbage collector for memory management.^[70] It uses dynamic name resolution (late binding), which binds method and variable names during program execution.

Its design offers some support for functional programming in the Lisp tradition. It has filter,mapandreduce functions; list comprehensions, dictionaries, sets, and generator expressions.^[71] The standard library has two modules (itertools and functools) that implement functional tools borrowed from Haskell and Standard ML.^[72]

Its core philosophy is summarized in the document The Zen of Python (PEP 20), which includes aphorisms such as:^[73]

• Beautiful is better than ugly.
• Explicit is better than implicit.
• Simple is better than complex.
• Complex is better than complicated.
• Readability counts.

Rather than building all of its functionality into its core, Python was designed to be highly extensible via modules. This compact modularity has made it particularly popular as a means of adding programmable interfaces to existing applications. Van Rossum’s vision of a small core language with a large standard library and easily extensible interpreter stemmed from his frustrations with ABC, which espoused the opposite approach.^[42]

Python strives for a simpler, less-cluttered syntax and grammar while giving developers a choice in their coding methodology. In contrast to Perl’s «there is more than one way to do it» motto, Python embraces a «there should be one—and preferably only one—obvious way to do it» philosophy.^[73] Alex Martelli, a Fellow at the Python Software Foundation and Python book author, wrote: «To describe something as ‘clever’ is not considered a compliment in the Python culture.»^[74]

Python’s developers strive to avoid premature optimization and reject patches to non-critical parts of the CPython reference implementation that would offer marginal increases in speed at the cost of clarity.^[75] When speed is important, a Python programmer can move time-critical functions to extension modules written in languages such as C; or use PyPy, a just-in-time compiler. Cython is also available, which translates a Python script into C and makes direct C-level API calls into the Python interpreter.

Python’s developers aim for it to be fun to use. This is reflected in its name—a tribute to the British comedy group Monty Python^[76]—and in occasionally playful approaches to tutorials and reference materials, such as the use of the terms «spam» and «eggs» (a reference to a Monty Python sketch) in examples, instead of the often-used «foo» and «bar».^[77][78]

A common neologism in the Python community is pythonic, which has a wide range of meanings related to program style. «Pythonic» code may use Python idioms well, be natural or show fluency in the language, or conform with Python’s minimalist philosophy and emphasis on readability. Code that is difficult to understand or reads like a rough transcription from another programming language is called unpythonic.^[79][80]

Syntax and semantics

Python is meant to be an easily readable language. Its formatting is visually uncluttered and often uses English keywords where other languages use punctuation. Unlike many other languages, it does not use curly brackets to delimit blocks, and semicolons after statements are allowed but rarely used. It has fewer syntactic exceptions and special cases than C or Pascal.^[81]

Indentation

Python uses whitespace indentation, rather than curly brackets or keywords, to delimit blocks. An increase in indentation comes after certain statements; a decrease in indentation signifies the end of the current block.^[82] Thus, the program’s visual structure accurately represents its semantic structure.^[83] This feature is sometimes termed the off-side rule. Some other languages use indentation this way; but in most, indentation has no semantic meaning. The recommended indent size is four spaces.^[84]

Statements and control flow

Python’s statements include:

• The assignment statement, using a single equals sign =
• The if statement, which conditionally executes a block of code, along with else and elif (a contraction of else-if)
• The for statement, which iterates over an iterable object, capturing each element to a local variable for use by the attached block
• The while statement, which executes a block of code as long as its condition is true
• The try statement, which allows exceptions raised in its attached code block to be caught and handled by except clauses (or new syntax except* in Python 3.11 for exception groups^[85]); it also ensures that clean-up code in a finally block is always run regardless of how the block exits
• The raise statement, used to raise a specified exception or re-raise a caught exception
• The class statement, which executes a block of code and attaches its local namespace to a class, for use in object-oriented programming
• The def statement, which defines a function or method
• The with statement, which encloses a code block within a context manager (for example, acquiring a lock before it is run, then releasing the lock; or opening and closing a file), allowing resource-acquisition-is-initialization (RAII)-like behavior and replacing a common try/finally idiom^[86]
• The break statement, which exits a loop
• The continue statement, which skips the rest of the current iteration and continues with the next
• The del statement, which removes a variable—deleting the reference from the name to the value, and producing an error if the variable is referred to before it is redefined
• The pass statement, serving as a NOP, syntactically needed to create an empty code block
• The assert statement, used in debugging to check for conditions that should apply
• The yield statement, which returns a value from a generator function (and also an operator); used to implement coroutines
• The return statement, used to return a value from a function
• The import and from statements, used to import modules whose functions or variables can be used in the current program

The assignment statement (=) binds a name as a reference to a separate, dynamically allocated object. Variables may subsequently be rebound at any time to any object. In Python, a variable name is a generic reference holder without a fixed data type; however, it always refers to some object with a type. This is called dynamic typing—in contrast to statically-typed languages, where each variable may contain only a value of a certain type.

Python does not support tail call optimization or first-class continuations, and, according to Van Rossum, it never will.^[87][88] However, better support for coroutine-like functionality is provided by extending Python’s generators.^[89] Before 2.5, generators were lazy iterators; data was passed unidirectionally out of the generator. From Python 2.5 on, it is possible to pass data back into a generator function; and from version 3.3, it can be passed through multiple stack levels.^[90]

Expressions

Python’s expressions include:

• The +, -, and * operators for mathematical addition, subtraction, and multiplication are similar to other languages, but the behavior of division differs. There are two types of divisions in Python: floor division (or integer division) // and floating-point/division.^[91] Python uses the ** operator for exponentiation.
• Python uses the + operator for string concatenation. Python uses the * operator for duplicating a string a specified number of times.
• The @ infix operator. It is intended to be used by libraries such as NumPy for matrix multiplication.^[92][93]
• The syntax :=, called the «walrus operator», was introduced in Python 3.8. It assigns values to variables as part of a larger expression.^[94]
• In Python, == compares by value. Python’s is operator may be used to compare object identities (comparison by reference), and comparisons may be chained—for example, a <= b <= c.
• Python uses and, or, and not as boolean operators.
• Python has a type of expression called a list comprehension, as well as a more general expression called a generator expression.^[71]
• Anonymous functions are implemented using lambda expressions; however, there may be only one expression in each body.
• Conditional expressions are written as x if c else y^[95] (different in order of operands from the c ? x : y operator common to many other languages).
• Python makes a distinction between lists and tuples. Lists are written as [1, 2, 3], are mutable, and cannot be used as the keys of dictionaries (dictionary keys must be immutable in Python). Tuples, written as (1, 2, 3), are immutable and thus can be used as keys of dictionaries, provided all of the tuple’s elements are immutable. The + operator can be used to concatenate two tuples, which does not directly modify their contents, but produces a new tuple containing the elements of both. Thus, given the variable t initially equal to (1, 2, 3), executing t = t + (4, 5) first evaluates t + (4, 5), which yields (1, 2, 3, 4, 5), which is then assigned back to t—thereby effectively «modifying the contents» of t while conforming to the immutable nature of tuple objects. Parentheses are optional for tuples in unambiguous contexts.^[96]
• Python features sequence unpacking where multiple expressions, each evaluating to anything that can be assigned (to a variable, writable property, etc.) are associated in an identical manner to that forming tuple literals—and, as a whole, are put on the left-hand side of the equal sign in an assignment statement. The statement expects an iterable object on the right-hand side of the equal sign that produces the same number of values as the provided writable expressions; when iterated through them, it assigns each of the produced values to the corresponding expression on the left.^[97]
• Python has a «string format» operator % that functions analogously to printf format strings in C—e.g. "spam=%s eggs=%d" % ("blah", 2) evaluates to "spam=blah eggs=2". In Python 2.6+ and 3+, this was supplemented by the format() method of the str class, e.g. "spam={0} eggs={1}".format("blah", 2). Python 3.6 added «f-strings»: spam = "blah"; eggs = 2; f'spam={spam} eggs={eggs}'.^[98]
• Strings in Python can be concatenated by «adding» them (with the same operator as for adding integers and floats), e.g. "spam" + "eggs" returns "spameggs". If strings contain numbers, they are added as strings rather than integers, e.g. "2" + "2" returns "22".
• Python has various string literals:
  • Delimited by single or double quote marks; unlike in Unix shells, Perl, and Perl-influenced languages, single and double quote marks work the same. Both use the backslash () as an escape character. String interpolation became available in Python 3.6 as «formatted string literals».^[98]
  • Triple-quoted (beginning and ending with three single or double quote marks), which may span multiple lines and function like here documents in shells, Perl, and Ruby.
  • Raw string varieties, denoted by prefixing the string literal with r. Escape sequences are not interpreted; hence raw strings are useful where literal backslashes are common, such as regular expressions and Windows-style paths. (Compare «@-quoting» in C#.)
• Python has array index and array slicing expressions in lists, denoted as a[key], a[start:stop] or a[start:stop:step]. Indexes are zero-based, and negative indexes are relative to the end. Slices take elements from the start index up to, but not including, the stop index. The third slice parameter called step or stride, allows elements to be skipped and reversed. Slice indexes may be omitted—for example, a[:] returns a copy of the entire list. Each element of a slice is a shallow copy.

In Python, a distinction between expressions and statements is rigidly enforced, in contrast to languages such as Common Lisp, Scheme, or Ruby. This leads to duplicating some functionality. For example:

• List comprehensions vs. for-loops
• Conditional expressions vs. if blocks
• The eval() vs. exec() built-in functions (in Python 2, exec is a statement); the former is for expressions, the latter is for statements

Statements cannot be a part of an expression—so list and other comprehensions or lambda expressions, all being expressions, cannot contain statements. A particular case is that an assignment statement such as a = 1 cannot form part of the conditional expression of a conditional statement. This has the advantage of avoiding a classic C error of mistaking an assignment operator = for an equality operator == in conditions: if (c = 1) { ... } is syntactically valid (but probably unintended) C code, but if c = 1: ... causes a syntax error in Python.

Methods

Methods on objects are functions attached to the object’s class; the syntax instance.method(argument) is, for normal methods and functions, syntactic sugar for Class.method(instance, argument). Python methods have an explicit self parameter to access instance data, in contrast to the implicit self (or this) in some other object-oriented programming languages (e.g., C++, Java, Objective-C, Ruby).^[99] Python also provides methods, often called dunder methods (due to their names beginning and ending with double-underscores), to allow user-defined classes to modify how they are handled by native operations including length, comparison, in arithmetic operations and type conversion.^[100]

Typing

Python uses duck typing and has typed objects but untyped variable names. Type constraints are not checked at compile time; rather, operations on an object may fail, signifying that it is not of a suitable type. Despite being dynamically typed, Python is strongly typed, forbidding operations that are not well-defined (for example, adding a number to a string) rather than silently attempting to make sense of them.

Python allows programmers to define their own types using classes, most often used for object-oriented programming. New instances of classes are constructed by calling the class (for example, SpamClass() or EggsClass()), and the classes are instances of the metaclass type (itself an instance of itself), allowing metaprogramming and reflection.

Before version 3.0, Python had two kinds of classes (both using the same syntax): old-style and new-style,^[101] current Python versions only support the semantics new style.

Python supports gradual typing.^[102] Python’s syntax allows specifying static types, but they are not checked in the default implementation, CPython. An experimental optional static type-checker, mypy, supports compile-time type checking.^[103]

"""Spanning
multiple
lines"""

Spanning
multiple
lines

Arithmetic operations

Python has the usual symbols for arithmetic operators (+, -, *, /), the floor division operator // and the modulo operation % (where the remainder can be negative, e.g. 4 % -3 == -2). It also has ** for exponentiation, e.g. 5**3 == 125 and 9**0.5 == 3.0, and a matrix‑multiplication operator @ .^[107] These operators work like in traditional math; with the same precedence rules, the operators infix (+ and - can also be unary to represent positive and negative numbers respectively).

The division between integers produces floating-point results. The behavior of division has changed significantly over time:^[108]

• Current Python (i.e. since 3.0) changed / to always be floating-point division, e.g. 5/2 == 2.5.
• The floor division // operator was introduced. So 7//3 == 2, -7//3 == -3, 7.5//3 == 2.0 and -7.5//3 == -3.0. Adding from __future__ import division causes a module used in Python 2.7 to use Python 3.0 rules for division (see above).

In Python terms, / is true division (or simply division), and // is floor division. / before version 3.0 is classic division.^[108]

Rounding towards negative infinity, though different from most languages, adds consistency. For instance, it means that the equation (a + b)//b == a//b + 1 is always true. It also means that the equation b*(a//b) + a%b == a is valid for both positive and negative values of a. However, maintaining the validity of this equation means that while the result of a%b is, as expected, in the half-open interval [0, b), where b is a positive integer, it has to lie in the interval (b, 0] when b is negative.^[109]

Python provides a round function for rounding a float to the nearest integer. For tie-breaking, Python 3 uses round to even: round(1.5) and round(2.5) both produce 2.^[110] Versions before 3 used round-away-from-zero: round(0.5) is 1.0, round(-0.5) is −1.0.^[111]

Python allows boolean expressions with multiple equality relations in a manner that is consistent with general use in mathematics. For example, the expression a < b < c tests whether a is less than b and b is less than c.^[112] C-derived languages interpret this expression differently: in C, the expression would first evaluate a < b, resulting in 0 or 1, and that result would then be compared with c.^[113]

Python uses arbitrary-precision arithmetic for all integer operations. The Decimal type/class in the decimal module provides decimal floating-point numbers to a pre-defined arbitrary precision and several rounding modes.^[114] The Fraction class in the fractions module provides arbitrary precision for rational numbers.^[115]

Due to Python’s extensive mathematics library, and the third-party library NumPy that further extends the native capabilities, it is frequently used as a scientific scripting language to aid in problems such as numerical data processing and manipulation.^[116][117]

Programming examples

Hello world program:

Program to calculate the factorial of a positive integer:

n = int(input('Type a number, and its factorial will be printed: '))

if n < 0:
    raise ValueError('You must enter a non-negative integer')

factorial = 1
for i in range(2, n + 1):
    factorial *= i

print(factorial)

Libraries

Python’s large standard library^[118] provides tools suited to many tasks and is commonly cited as one of its greatest strengths. For Internet-facing applications, many standard formats and protocols such as MIME and HTTP are supported. It includes modules for creating graphical user interfaces, connecting to relational databases, generating pseudorandom numbers, arithmetic with arbitrary-precision decimals,^[119] manipulating regular expressions, and unit testing.

Some parts of the standard library are covered by specifications—for example, the Web Server Gateway Interface (WSGI) implementation wsgiref follows PEP 333^[120]—but most are specified by their code, internal documentation, and test suites. However, because most of the standard library is cross-platform Python code, only a few modules need altering or rewriting for variant implementations.

As of 14 November 2022, the Python Package Index (PyPI), the official repository for third-party Python software, contains over 415,000^[121] packages with a wide range of functionality, including:

Development environments

Most Python implementations (including CPython) include a read–eval–print loop (REPL), permitting them to function as a command line interpreter for which users enter statements sequentially and receive results immediately.

Python also comes with an Integrated development environment (IDE) called IDLE, which is more beginner-oriented.

Other shells, including IDLE and IPython, add further abilities such as improved auto-completion, session state retention, and syntax highlighting.

As well as standard desktop integrated development environments, there are Web browser-based IDEs, including SageMath, for developing science- and math-related programs; PythonAnywhere, a browser-based IDE and hosting environment; and Canopy IDE, a commercial IDE emphasizing scientific computing.^[122]

Implementations

Reference implementation

CPython is the reference implementation of Python. It is written in C, meeting the C89 standard (Python 3.11 uses C11^[123]) with several select C99 features (With later C versions out, it is considered outdated.^[124][125] CPython includes its own C extensions, but third-party extensions are not limited to older C versions—e.g. they can be implemented with C11 or C++.^[126][127]) It compiles Python programs into an intermediate bytecode^[128] which is then executed by its virtual machine.^[129] CPython is distributed with a large standard library written in a mixture of C and native Python, and is available for many platforms, including Windows (starting with Python 3.9, the Python installer deliberately fails to install on Windows 7 and 8;^[130][131] Windows XP was supported until Python 3.5) and most modern Unix-like systems, including macOS (and Apple M1 Macs, since Python 3.9.1, with experimental installer) and unofficial support for e.g. VMS.^[132] Platform portability was one of its earliest priorities.^[133] (During Python 1 and 2 development, even OS/2 and Solaris were supported,^[134] but support has since been dropped for many platforms.)

Other implementations

• PyPy is a fast, compliant interpreter of Python 2.7 and 3.8.^[135][136] Its just-in-time compiler often brings a significant speed improvement over CPython but some libraries written in C cannot be used with it.^[137]
• Stackless Python is a significant fork of CPython that implements microthreads; it does not use the call stack in the same way, thus allowing massively concurrent programs. PyPy also has a stackless version.^[138]
• MicroPython and CircuitPython are Python 3 variants optimized for microcontrollers, including Lego Mindstorms EV3.^[139]
• Pyston is a variant of the Python runtime that uses just-in-time compilation to speed up the execution of Python programs.^[140]
• Cinder is a performance-oriented fork of CPython 3.8 that contains a number of optimizations including bytecode inline caching, eager evaluation of coroutines, a method-at-a-time JIT, and an experimental bytecode compiler.^[141]

Unsupported implementations

Other just-in-time Python compilers have been developed, but are now unsupported:

• Google began a project named Unladen Swallow in 2009, with the aim of speeding up the Python interpreter fivefold by using the LLVM, and of improving its multithreading ability to scale to thousands of cores,^[142] while ordinary implementations suffer from the global interpreter lock.
• Psyco is a discontinued just-in-time specializing compiler that integrates with CPython and transforms bytecode to machine code at runtime. The emitted code is specialized for certain data types and is faster than the standard Python code. Psyco does not support Python 2.7 or later.
• PyS60 was a Python 2 interpreter for Series 60 mobile phones released by Nokia in 2005. It implemented many of the modules from the standard library and some additional modules for integrating with the Symbian operating system. The Nokia N900 also supports Python with GTK widget libraries, enabling programs to be written and run on the target device.^[143]

Cross-compilers to other languages

There are several compilers to high-level object languages, with either unrestricted Python, a restricted subset of Python, or a language similar to Python as the source language:

• Brython,^[144] Transcrypt^[145][146] and Pyjs (latest release in 2012) compile Python to JavaScript.
• Cython compiles (a superset of) Python to C (while the resulting code is also usable with Python and also e.g. C++).
• Nuitka compiles Python into C.^[147]
• Numba uses LLVM to compile a subset of Python to machine code.
• Pythran compiles a subset of Python 3 to C++ (C++11).^{[148][149][150]}
• RPython can be compiled to C, and is used to build the PyPy interpreter of Python.
• The Python → 11l → C++ transpiler^[151] compiles a subset of Python 3 to C++ (C++17).

Specialized:

• MyHDL is a Python-based hardware description language (HDL), that converts MyHDL code to Verilog or VHDL code.

Older projects (or not to be used with Python 3.x and latest syntax):

• Google’s Grumpy (latest release in 2017) transpiles Python 2 to Go.^{[152][153][154]}
• IronPython allows running Python 2.7 programs (and an alpha, released in 2021, is also available for «Python 3.4, although features and behaviors from later versions may be included»^[155]) on the .NET Common Language Runtime.^[156]
• Jython compiles Python 2.7 to Java bytecode, allowing the use of the Java libraries from a Python program.^[157]
• Pyrex (latest release in 2010) and Shed Skin (latest release in 2013) compile to C and C++ respectively.

Performance

Performance comparison of various Python implementations on a non-numerical (combinatorial) workload was presented at EuroSciPy ’13.^[158] Python’s performance compared to other programming languages is also benchmarked by The Computer Language Benchmarks Game.^[159]

Development

Python’s development is conducted largely through the Python Enhancement Proposal (PEP) process, the primary mechanism for proposing major new features, collecting community input on issues, and documenting Python design decisions.^[160] Python coding style is covered in PEP 8.^[161] Outstanding PEPs are reviewed and commented on by the Python community and the steering council.^[160]

Enhancement of the language corresponds with the development of the CPython reference implementation. The mailing list python-dev is the primary forum for the language’s development. Specific issues were originally discussed in the Roundup bug tracker hosted at by the foundation.^[162] In 2022, all issues and discussions were migrated to GitHub.^[163] Development originally took place on a self-hosted source-code repository running Mercurial, until Python moved to GitHub in January 2017.^[164]

CPython’s public releases come in three types, distinguished by which part of the version number is incremented:

• Backward-incompatible versions, where code is expected to break and needs to be manually ported. The first part of the version number is incremented. These releases happen infrequently—version 3.0 was released 8 years after 2.0. According to Guido van Rossum, a version 4.0 is very unlikely to ever happen.^[165]
• Major or «feature» releases are largely compatible with the previous version but introduce new features. The second part of the version number is incremented. Starting with Python 3.9, these releases are expected to happen annually.^[166][167] Each major version is supported by bug fixes for several years after its release.^[168]
• Bugfix releases,^[169] which introduce no new features, occur about every 3 months and are made when a sufficient number of bugs have been fixed upstream since the last release. Security vulnerabilities are also patched in these releases. The third and final part of the version number is incremented.^[169]

Many alpha, beta, and release-candidates are also released as previews and for testing before final releases. Although there is a rough schedule for each release, they are often delayed if the code is not ready. Python’s development team monitors the state of the code by running the large unit test suite during development.^[170]

The major academic conference on Python is PyCon. There are also special Python mentoring programs, such as Pyladies.

Python 3.10 deprecated wstr (to be removed in Python 3.12; meaning Python extensions^[171] need to be modified by then),^[172] and added pattern matching to the language.^[173]

API documentation generators

Tools that can generate documentation for Python API include pydoc (available as part of the standard library), Sphinx, Pdoc and its forks, Doxygen and Graphviz, among others.^[174]

Naming

Python’s name is derived from the British comedy group Monty Python, whom Python creator Guido van Rossum enjoyed while developing the language. Monty Python references appear frequently in Python code and culture;^[175] for example, the metasyntactic variables often used in Python literature are spam and eggs instead of the traditional foo and bar.^[175][176] The official Python documentation also contains various references to Monty Python routines.^[177][178]

The prefix Py- is used to show that something is related to Python. Examples of the use of this prefix in names of Python applications or libraries include Pygame, a binding of SDL to Python (commonly used to create games); PyQt and PyGTK, which bind Qt and GTK to Python respectively; and PyPy, a Python implementation originally written in Python.

Popularity

Since 2003, Python has consistently ranked in the top ten most popular programming languages in the TIOBE Programming Community Index where as of December 2022 it was the most popular language (ahead of C, C++, and Java).^[40] It was selected Programming Language of the Year (for «the highest rise in ratings in a year») in 2007, 2010, 2018, and 2020 (the only language to have done so four times as of 2020^[179]).

An empirical study found that scripting languages, such as Python, are more productive than conventional languages, such as C and Java, for programming problems involving string manipulation and search in a dictionary, and determined that memory consumption was often «better than Java and not much worse than C or C++».^[180]

Large organizations that use Python include Wikipedia, Google,^[181] Yahoo!,^[182] CERN,^[183] NASA,^[184] Facebook,^[185] Amazon, Instagram,^[186] Spotify,^[187] and some smaller entities like ILM^[188] and ITA.^[189] The social news networking site Reddit was written mostly in Python.^[190]

Uses

Python can serve as a scripting language for web applications, e.g., via mod_wsgi for the Apache webserver.^[191] With Web Server Gateway Interface, a standard API has evolved to facilitate these applications. Web frameworks like Django, Pylons, Pyramid, TurboGears, web2py, Tornado, Flask, Bottle, and Zope support developers in the design and maintenance of complex applications. Pyjs and IronPython can be used to develop the client-side of Ajax-based applications. SQLAlchemy can be used as a data mapper to a relational database. Twisted is a framework to program communications between computers, and is used (for example) by Dropbox.

Libraries such as NumPy, SciPy, and Matplotlib allow the effective use of Python in scientific computing,^[192][193] with specialized libraries such as Biopython and Astropy providing domain-specific functionality. SageMath is a computer algebra system with a notebook interface programmable in Python: its library covers many aspects of mathematics, including algebra, combinatorics, numerical mathematics, number theory, and calculus.^[194] OpenCV has Python bindings with a rich set of features for computer vision and image processing.^[195]

Python is commonly used in artificial intelligence projects and machine learning projects with the help of libraries like TensorFlow, Keras, Pytorch, and scikit-learn.^{[196][197][198][199]} As a scripting language with a modular architecture, simple syntax, and rich text processing tools, Python is often used for natural language processing.^[200]

Python can also be used to create games, with libraries such as Pygame, which can make 2D games.

Python has been successfully embedded in many software products as a scripting language, including in finite element method software such as Abaqus, 3D parametric modelers like FreeCAD, 3D animation packages such as 3ds Max, Blender, Cinema 4D, Lightwave, Houdini, Maya, modo, MotionBuilder, Softimage, the visual effects compositor Nuke, 2D imaging programs like GIMP,^[201] Inkscape, Scribus and Paint Shop Pro,^[202] and musical notation programs like scorewriter and capella. GNU Debugger uses Python as a pretty printer to show complex structures such as C++ containers. Esri promotes Python as the best choice for writing scripts in ArcGIS.^[203] It has also been used in several video games,^[204][205] and has been adopted as first of the three available programming languages in Google App Engine, the other two being Java and Go.^[206]

Many operating systems include Python as a standard component. It ships with most Linux distributions,^[207] AmigaOS 4 (using Python 2.7), FreeBSD (as a package), NetBSD, and OpenBSD (as a package) and can be used from the command line (terminal). Many Linux distributions use installers written in Python: Ubuntu uses the Ubiquity installer, while Red Hat Linux and Fedora Linux use the Anaconda installer. Gentoo Linux uses Python in its package management system, Portage.

Python is used extensively in the information security industry, including in exploit development.^[208][209]

Most of the Sugar software for the One Laptop per Child XO, developed at Sugar Labs since 2008, is written in Python.^[210] The Raspberry Pi single-board computer project has adopted Python as its main user-programming language.

LibreOffice includes Python and intends to replace Java with Python. Its Python Scripting Provider is a core feature^[211] since Version 4.0 from 7 February 2013.

Languages influenced by Python

Python’s design and philosophy have influenced many other programming languages:

• Boo uses indentation, a similar syntax, and a similar object model.^[212]
• Cobra uses indentation and a similar syntax, and its Acknowledgements document lists Python first among languages that influenced it.^[213]
• CoffeeScript, a programming language that cross-compiles to JavaScript, has Python-inspired syntax.
• ECMAScript/JavaScript borrowed iterators and generators from Python.^[214]
• GDScript, a scripting language very similar to Python, built-in to the Godot game engine.^[215]
• Go is designed for the «speed of working in a dynamic language like Python»^[216] and shares the same syntax for slicing arrays.
• Groovy was motivated by the desire to bring the Python design philosophy to Java.^[217]
• Julia was designed to be «as usable for general programming as Python».^[29]
• Nim uses indentation and similar syntax.^[218]
• Ruby’s creator, Yukihiro Matsumoto, has said: «I wanted a scripting language that was more powerful than Perl, and more object-oriented than Python. That’s why I decided to design my own language.»^[219]
• Swift, a programming language developed by Apple, has some Python-inspired syntax.^[220]

Python’s development practices have also been emulated by other languages. For example, the practice of requiring a document describing the rationale for, and issues surrounding, a change to the language (in Python, a PEP) is also used in Tcl,^[221] Erlang,^[222] and Swift.^[223]

See also

• Python syntax and semantics
• pip (package manager)
• List of programming languages
• History of programming languages
• Comparison of programming languages

References

Sources

• «Python for Artificial Intelligence». Wiki.python.org. 19 July 2012. Archived from the original on 1 November 2012. Retrieved 3 December 2012.
• Paine, Jocelyn, ed. (August 2005). «AI in Python». AI Expert Newsletter. Amzi!. Archived from the original on 26 March 2012. Retrieved 11 February 2012.
• «PyAIML 0.8.5 : Python Package Index». Pypi.python.org. Retrieved 17 July 2013.
• Russell, Stuart J. & Norvig, Peter (2009). Artificial Intelligence: A Modern Approach (3rd ed.). Upper Saddle River, NJ: Prentice Hall. ISBN 978-0-13-604259-4.

Further reading

• Downey, Allen B. (May 2012). Think Python: How to Think Like a Computer Scientist (version 1.6.6 ed.). ISBN 978-0-521-72596-5.
• Hamilton, Naomi (5 August 2008). «The A-Z of Programming Languages: Python». Computerworld. Archived from the original on 29 December 2008. Retrieved 31 March 2010.
• Lutz, Mark (2013). Learning Python (5th ed.). O’Reilly Media. ISBN 978-0-596-15806-4.
• Summerfield, Mark (2009). Programming in Python 3 (2nd ed.). Addison-Wesley Professional. ISBN 978-0-321-68056-3.
• Ramalho, Luciano (May 2022). Fluent Python (2nd ed.). O’Reilly Media. ISBN 978-1-4920-5632-4.

External links

• Official website

Время на прочтение
9 мин

Количество просмотров 1.2M

На сайте Poromenos’ Stuff была
опубликована статья, в которой, в сжатой форме,
рассказывают об основах языка Python. Я предлагаю вам перевод этой статьи. Перевод не дословный. Я постарался подробнее объяснить некоторые моменты, которые могут быть непонятны.

Если вы собрались изучать язык Python, но не можете найти подходящего руководства, то эта
статья вам очень пригодится! За короткое время, вы сможете познакомиться с
основами языка Python. Хотя эта статья часто опирается
на то, что вы уже имеете опыт программирования, но, я надеюсь, даже новичкам
этот материал будет полезен. Внимательно прочитайте каждый параграф. В связи с
сжатостью материала, некоторые темы рассмотрены поверхностно, но содержат весь
необходимый метриал.

Основные свойства

Python не требует явного объявления переменных, является регистро-зависим (переменная var не эквивалентна переменной Var или VAR — это три разные переменные) объектно-ориентированным языком.

Синтаксис

Во первых стоит отметить интересную особенность Python. Он не содержит операторных скобок (begin..end в pascal или {..}в Си), вместо этого блоки выделяются отступами: пробелами или табуляцией, а вход в блок из операторов осуществляется двоеточием. Однострочные комментарии начинаются со знака фунта «#», многострочные — начинаются и заканчиваются тремя двойными кавычками «»»»».
Чтобы присвоить значение пременной используется знак «=», а для сравнения —
«==». Для увеличения значения переменной, или добавления к строке используется оператор «+=», а для уменьшения — «-=». Все эти операции могут взаимодействовать с большинством типов, в том числе со строками. Например

>>> myvar = 3
>>> myvar += 2
>>> myvar -= 1
«»«Это многострочный комментарий
Строки заключенные в три двойные кавычки игнорируются»»»
>>> mystring = «Hello»
>>> mystring += » world.»
>>> print mystring
Hello world.
# Следующая строка меняет
значения переменных местами. (Всего одна строка!)
>>> myvar, mystring = mystring, myvar

Структуры данных

Python содержит такие структуры данных как списки (lists), кортежи (tuples) и словари (dictionaries). Списки — похожи на одномерные массивы (но вы можете использовать Список включающий списки — многомерный массив), кортежи — неизменяемые списки, словари — тоже списки, но индексы могут быть любого типа, а не только числовыми. «Массивы» в Python могут содержать данные любого типа, то есть в одном массиве может могут находиться числовые, строковые и другие типы данных. Массивы начинаются с индекса 0, а последний элемент можно получить по индексу -1 Вы можете присваивать переменным функции и использовать их соответственно.

>>> sample = [1, [«another», «list»], («a», «tuple»)] #Список состоит из целого числа, другого списка и кортежа
>>> mylist = [«List item 1», 2, 3.14] #Этот список содержит строку, целое и дробное число
>>> mylist[0] = «List item 1 again» #Изменяем первый (нулевой) элемент листа mylist
>>> mylist[-1] = 3.14 #Изменяем последний элемент листа
>>> mydict = {«Key 1»: «Value 1», 2: 3, «pi»: 3.14} #Создаем словарь, с числовыми и целочисленным индексами
>>> mydict[«pi»] = 3.15 #Изменяем элемент словаря под индексом «pi».
>>> mytuple = (1, 2, 3) #Задаем кортеж
>>> myfunction = len #Python позволяет таким образом объявлять синонимы функции
>>> print myfunction(list)
3

Вы можете использовать часть массива, задавая первый и последний индекс через двоеточие «:». В таком случае вы получите часть массива, от первого индекса до второго не включительно. Если не указан первый элемент, то отсчет начинается с начала массива, а если не указан последний — то масив считывается до последнего элемента. Отрицательные значения определяют положение элемента с конца. Например:

>>> mylist = [«List item 1», 2, 3.14]
>>> print mylist[:] #Считываются все элементы массива
[‘List item 1’, 2, 3.1400000000000001]
>>> print mylist[0:2] #Считываются нулевой и первый элемент массива.
[‘List item 1’, 2]
>>> print mylist[-3:-1] #Считываются элементы от нулевого (-3) до второго (-1) (не включительно)
[‘List item 1’, 2]
>>> print mylist[1:] #Считываются элементы от первого, до последнего
[2, 3.14]

Строки

Строки в Python обособляются кавычками двойными «»» или одинарными «’». Внутри двойных ковычек могут присутствовать одинарные или наоборот. К примеру строка «Он сказал ‘привет’!» будет выведена на экран как «Он сказал ‘привет’!». Если нужно использовать строку из несколько строчек, то эту строку надо начинать и заканчивать тремя двойными кавычками «»»»». Вы можете подставить в шаблон строки элементы из кортежа или словаря. Знак процента «%» между строкой и кортежем, заменяет в строке символы «%s» на элемент кортежа. Словари позволяют вставлять в строку элемент под заданным индексом. Для этого надо использовать в строке конструкцию «%(индекс)s». В этом случае вместо «%(индекс)s» будет подставлено значение словаря под заданным индексом.

>>>print «Name: %snNumber: %snString: %s» % (myclass.name, 3, 3 * «-«)
Name: Poromenos
Number: 3
String: —  
strString = «»«Этот текст расположен
на нескольких строках»»»

 
>>>

print «This %(verb)s a %(noun)s.» % {«noun»: «test», «verb»: «is»}
This is a test.

Операторы

Операторы while, if, for составляют операторы перемещения. Здесь нет аналога оператора select, так что придется обходиться if. В операторе for происходит сравнение переменной и списка. Чтобы получить список цифр до числа <number> — используйте функцию range(<number>). Вот пример использования операторов

rangelist = range(10) #Получаем список из десяти цифр (от 0 до 9)
>>> print rangelist
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
for number in rangelist: #Пока переменная number (которая каждый раз увеличивается на единицу) входит в список…
# Проверяем входит ли переменная
# numbers в кортеж чисел (3, 4, 7, 9)
if number in (3, 4, 7, 9): #Если переменная number входит в кортеж (3, 4, 7, 9)…
# Операция «break» обеспечивает
# выход из цикла в любой момент
break
else:
# «continue» осуществляет «прокрутку»
# цикла. Здесь это не требуется, так как после этой операции
# в любом случае программа переходит опять к обработке цикла
continue
else:
# «else» указывать необязательно. Условие выполняется
# если цикл не был прерван при помощи «break».
pass # Ничего не делатьif rangelist[1] == 2:
print «The second item (lists are 0-based) is 2»
elif rangelist[1] == 3:
print «The second item (lists are 0-based) is 3»
else:
print «Dunno»while rangelist[1] == 1:
pass

Функции

Для объявления функции служит ключевое слово «def». Аргументы функции задаются в скобках после названия функции. Можно задавать необязательные аргументы, присваивая им значение по умолчанию. Функции могут возвращать кортежи, в таком случае надо писать возвращаемые значения через запятую. Ключевое слово «lambda» служит для объявления элементарных функций .

# arg2 и arg3 — необязательые аргументы, принимают значение объявленное по умолчни,
# если не задать им другое значение при вызове функци.
def myfunction(arg1, arg2 = 100, arg3 = «test»):
return arg3, arg2, arg1
#Функция вызывается со значением первого аргумента — «Argument 1», второго — по умолчанию, и третьего — «Named argument».
>>>ret1, ret2, ret3 = myfunction(«Argument 1», arg3 = «Named argument»)
# ret1, ret2 и ret3 принимают значения «Named argument», 100, «Argument 1» соответственно
>>> print ret1, ret2, ret3
Named argument 100 Argument 1# Следующая запись эквивалентна def f(x): return x + 1
functionvar = lambda x: x + 1
>>> print functionvar(1)
2

Классы

Язык Python ограничен в множественном наследовании в классах. Внутренние переменные и внутренние методы классов начинаются с двух знаков нижнего подчеркивания «__» (например «__myprivatevar»). Мы можем также присвоить значение переменной класса извне. Пример:

class Myclass:
common = 10
def __init__(self):
self.myvariable = 3
def myfunction(self, arg1, arg2):
return self.myvariable# Здесь мы объявили класс Myclass. Функция __init__ вызывается автоматически при инициализации классов.
>>> classinstance = Myclass() # Мы инициализировали класс и переменная myvariable приобрела значение 3 как заявлено в методе инициализации
>>> classinstance.myfunction(1, 2) #Метод myfunction класса Myclass возвращает значение переменной myvariable
3
# Переменная common объявлена во всех классах
>>> classinstance2 = Myclass()
>>> classinstance.common
10
>>> classinstance2.common
10
# Поэтому, если мы изменим ее значение в классе Myclass изменятся
# и ее значения в объектах, инициализированных классом Myclass
>>> Myclass.common = 30
>>> classinstance.common
30
>>> classinstance2.common
30
# А здесь мы не изменяем переменную класса. Вместо этого
# мы объявляем оную в объекте и присваиваем ей новое значение
>>> classinstance.common = 10
>>> classinstance.common
10
>>> classinstance2.common
30
>>> Myclass.common = 50
# Теперь изменение переменной класса не коснется
# переменных объектов этого класса
>>> classinstance.common
10
>>> classinstance2.common
50# Следующий класс является наследником класса Myclass
# наследуя его свойства и методы, ктому же класс может
# наследоваться из нескольких классов, в этом случае запись
# такая: class Otherclass(Myclass1, Myclass2, MyclassN)
class Otherclass(Myclass):
def __init__(self, arg1):
self.myvariable = 3
print arg1

 
>>> classinstance = Otherclass(

«hello»)
hello
>>> classinstance.myfunction(1, 2)
3
# Этот класс не имеет совйтсва test, но мы можем
# объявить такую переменную для объекта. Причем
# tэта переменная будет членом только classinstance.
>>> classinstance.test = 10
>>> classinstance.test
10

Исключения

Исключения в Python имеют структуру try—except [exceptionname]:

def somefunction():
try:
# Деление на ноль вызывает ошибку
10 / 0
except ZeroDivisionError:
# Но программа не «Выполняет недопустимую операцию»
# А обрабатывает блок исключения соответствующий ошибке «ZeroDivisionError»
print «Oops, invalid.»

 
>>> fnexcept()
Oops, invalid.

Импорт

Внешние библиотеки можно подключить процедурой «import [libname]», где [libname] — название подключаемой библиотеки. Вы так же можете использовать команду «from [libname] import [funcname]», чтобы вы могли использовать функцию [funcname] из библиотеки [libname]

import random #Импортируем библиотеку «random»
from time import clock #И заодно функцию «clock» из библиотеки «time»

 
randomint =

random.randint(1, 100)
>>> print randomint
64

Работа с файловой системой

Python имеет много встроенных библиотек. В этом примере мы попробуем сохранить в бинарном файле структуру списка, прочитать ее и сохраним строку в текстовом файле. Для преобразования структуры данных мы будем использовать стандартную библиотеку «pickle»

import pickle
mylist = [«This», «is», 4, 13327]
# Откроем файл C:binary.dat для записи. Символ «r»
# предотвращает замену специальных сиволов (таких как n, t, b и др.).
myfile = file(r«C:binary.dat», «w»)
pickle.dump(mylist, myfile)
myfile.close()

 
myfile =

file(r«C:text.txt», «w»)
myfile.write(«This is a sample string»)
myfile.close()

 
myfile =

file(r«C:text.txt»)
>>> print myfile.read()
‘This is a sample string’
myfile.close()# Открываем файл для чтения
myfile = file(r«C:binary.dat»)
loadedlist = pickle.load(myfile)
myfile.close()
>>> print loadedlist
[‘This’, ‘is’, 4, 13327]

Особенности

• Условия могут комбинироваться. 1 < a < 3 выполняется тогда, когда а больше 1, но меньше 3.
• Используйте операцию «del» чтобы очищать переменные или элементы массива.
• Python предлагает большие возможности для работы со списками. Вы можете использовать операторы объявлении структуры списка. Оператор for позволяет задавать элементы списка в определенной последовательности, а if — позволяет выбирать элементы по условию.

>>> lst1 = [1, 2, 3]
>>> lst2 = [3, 4, 5]
>>> print [x * y for x in lst1 for y in lst2]
[3, 4, 5, 6, 8, 10, 9, 12, 15]
>>> print [x for x in lst1 if 4 > x > 1]
[2, 3]
# Оператор «any» возвращает true, если хотя
# бы одно из условий, входящих в него, выполняется.
>>> any(i % 3 for i in [3, 3, 4, 4, 3])
True
# Следующая процедура подсчитывает количество
# подходящих элементов в списке
>>> sum(1 for i in [3, 3, 4, 4, 3] if i == 3)
3
>>> del lst1[0]
>>> print lst1
[2, 3]
>>> del lst1

• Глобальные переменные объявляются вне функций и могут быть прочитанны без каких либо объявлений. Но если вам необходимо изменить значение глобальной переменной из функции, то вам необходимо объявить ее в начале функции ключевым словом «global», если вы этого не сделаете, то Python объявит переменную, доступную только для этой функции.

number = 5def myfunc():
# Выводит 5
print numberdef anotherfunc():
# Это вызывает исключение, поскольку глобальная апеременная
# не была вызванна из функции. Python в этом случае создает
# одноименную переменную внутри этой функции и доступную
# только для операторов этой функции.
print number
number = 3def yetanotherfunc():
global number
# И только из этой функции значение переменной изменяется.
number = 3

Эпилог

Разумеется в этой статье не описываются все возможности Python. Я надеюсь что эта статья поможет вам, если вы захотите и в дальнейшем изучать этот язык программирования.

Преимущества Python

• Скорость выполнения программ написанных на Python очень высока. Это связанно с тем, что основные библиотеки Python
  написаны на C++ и выполнение задач занимает меньше времени, чем на других языках высокого уровня.
• В связи с этим вы можете писать свои собственные модули для Python на C или C++
• В стандартныx библиотеках Python вы можете найти средства для работы с электронной почтой, протоколами
  Интернета, FTP, HTTP, базами данных, и пр.
• Скрипты, написанные при помощи Python выполняются на большинстве современных ОС. Такая переносимость обеспечивает Python применение в самых различных областях.
• Python подходит для любых решений в области программирования, будь то офисные программы, вэб-приложения, GUI-приложения и т.д.
• Над разработкой Python трудились тысячи энтузиастов со всего мира. Поддержкой современных технологий в стандартных библиотеках мы можем быть обязаны именно тому, что Python был открыт для всех желающих.

Класс языка:	мультипарадигмальный: объектно-ориентированный, кроссплатформенный, рефлективный, императивный, функциональный, аспектно-ориентированный
Тип исполнения:	интерпретируемый, компилируемый в MSIL, компилируемый в байт-код Java
Появился в:	1990
Автор(ы):	Гвидо ван Россум
Расширение файлов:	.py, .pyw, .pyc, .pyo, .pyd[1]
Релиз:	2.7.3, 3.3.0 (10 апреля 2012[2], 29 сентября 2012[3])
Типизация данных:	строгая, динамическая
Основные реализации:	CPython, Jython, IronPython, PyPy, Stackless
Испытал влияние:	ABC, Modula-3, Lisp, Tcl Smalltalk, C, Java, Icon
Повлиял на:	Ruby, Boo, Groovy, ECMAScript, CoffeeScript
Лицензия	PSFL
Сайт:	www.python.org

Python (англ. python — питон, произносится [ˈpaɪθ⟨ə⟩n] — па́йтон; в русском языке распространено название пито́н^[4])^[5] — высокоуровневый язык программирования общего назначения, ориентированный на повышение производительности разработчика и читаемости кода. Синтаксис ядра Python минималистичен. В то же время стандартная библиотека включает большой объём полезных функций.

Python поддерживает несколько парадигм программирования, в том числе структурное, объектно-ориентированное, функциональное, императивное и аспектно-ориентированное. Основные архитектурные черты — динамическая типизация, автоматическое управление памятью, полная интроспекция, механизм обработки исключений, поддержка многопоточных вычислений и удобные высокоуровневые структуры данных. Код в Питоне организовывается в функции и классы, которые могут объединяться в модули (которые в свою очередь могут быть объединены в пакеты).

Эталонной реализацией Python является интерпретатор CPython, поддерживающий большинство активно используемых платформ^[6]. Он распространяется под свободной лицензией Python Software Foundation License, позволяющей использовать его без ограничений в любых приложениях, включая проприетарные^[7]. Есть реализации интерпретаторов для JVM (с возможностью компиляции), MSIL (с возможностью компиляции), LLVM и других. Проект PyPy предлагает реализацию Питона на самом Питоне, что уменьшает затраты на изменения языка и постановку экспериментов над новыми возможностями.

Python — активно развивающийся язык программирования, новые версии (с добавлением/изменением языковых свойств) выходят примерно раз в два с половиной года. Вследствие этого и некоторых других причин на Python отсутствуют ANSI, ISO или другие официальные стандарты, их роль выполняет CPython.

Философия

Разработчики языка Python придерживаются определённой философии программирования, называемой «The Zen of Python» («Дзэн Питона», или «Дзэн Пайтона»)^[8]. Её текст выдаётся интерпретатором Питона по команде import this (работает один раз за сессию). Автором этой философии считается Тим Пейтерс.

Текст философии:

Красивое лучше, чем уродливое. Явное лучше, чем неявное. Простое лучше, чем сложное. Сложное лучше, чем запутанное. Плоское лучше, чем вложенное. Разреженное лучше, чем плотное. Читаемость имеет значение. Особые случаи не настолько особые, чтобы нарушать правила. При этом практичность важнее безупречности. Ошибки никогда не должны замалчиваться. Если не замалчиваются явно. Встретив двусмысленность, отбрось искушение угадать. Должен существовать один — и, желательно, только один — очевидный способ сделать это. Хотя он поначалу может быть и не очевиден, если вы не голландец[9]. Сейчас лучше, чем никогда. Хотя никогда зачастую лучше, чем прямо сейчас. Если реализацию сложно объяснить — идея плоха. Если реализацию легко объяснить — идея, возможно, хороша. Пространства имён — отличная штука! Будем делать их побольше! Оригинальный текст  (англ.)   Beautiful is better than ugly. Explicit is better than implicit. Simple is better than complex. Complex is better than complicated. Flat is better than nested. Sparse is better than dense. Readability counts. Special cases aren’t special enough to break the rules. Although practicality beats purity. Errors should never pass silently. Unless explicitly silenced. In the face of ambiguity, refuse the temptation to guess. There should be one — and preferably only one — obvious way to do it. Although that way may not be obvious at first unless you’re Dutch. Now is better than never. Although never is often better than ‘right now’. If the implementation is hard to explain, it’s a bad idea. If the implementation is easy to explain, it may be a good idea. Namespaces are one honking great idea — let’s do more of those!

История

Разработка языка Python была начата в конце 1980-х годов^[10] сотрудником голландского института CWI Гвидо ван Россумом. Для распределённой ОС Amoeba требовался расширяемый скриптовый язык, и Гвидо начал писать Python на досуге, позаимствовав некоторые наработки для языка ABC (Гвидо участвовал в разработке этого языка, ориентированного на обучение программированию). В феврале 1991 года Гвидо опубликовал исходный текст в ньюсгруппе alt.sources^[11]. С самого начала Python проектировался как объектно-ориентированный язык.

Название языка произошло вовсе не от вида пресмыкающихся. Автор назвал язык в честь популярного британского комедийного телешоу 1970-х «Летающий цирк Монти Пайтона». Впрочем, всё равно название языка чаще ассоциируют именно со змеёй, нежели с фильмом — пиктограммы файлов в KDE или в Microsoft Windows и даже эмблема на сайте python.org (до выхода версии 2.5) изображают змеиные головы.

Наличие дружелюбного, отзывчивого сообщества пользователей считается наряду с дизайнерской интуицией Гвидо одним из факторов успеха Python. Развитие языка происходит согласно чётко регламентированному процессу создания, обсуждения, отбора и реализации документов PEP (англ. Python Enhancement Proposal) — предложений по развитию Python^[12].

3 декабря 2008 года^[13], после длительного тестирования, вышла первая версия Python 3000 (или Python 3.0, также используется сокращение Py3k). В Python 3000 устранены многие недостатки архитектуры с максимально возможным (но не полным) сохранением совместимости со старыми версиями Python. На сегодня поддерживаются обе ветви развития (Python 3.x и 2.x).

Влияние других языков на Python

Появившись сравнительно поздно, Python создавался под влиянием множества языков программирования:

• ABC — отступы для группировки операторов, высокоуровневые структуры данных (map)^[14][15] (Python фактически создавался как попытка исправить ошибки, допущенные при проектировании ABC);
• Modula-3 — пакеты, модули, использование else совместно с try и except, именованные аргументы функций (на это также повлиял Common Lisp);
• С, C++ — некоторые синтаксические конструкции (как пишет сам Гвидо ван Россум — он использовал наиболее непротиворечивые конструкции из С, чтобы не вызвать неприязнь у С-программистов к Python^[14]);
• Smalltalk — объектно-ориентированное программирование;
• Lisp — отдельные черты функционального программирования (lambda, map, reduce, filter и другие);
• Fortran — срезы массивов, комплексная арифметика;
• Miranda — списочные выражения;
• Java — модули logging, unittest, threading (часть возможностей оригинального модуля не реализована), xml.sax стандартной библиотеки, совместное использование finally и except при обработке исключений, использование @ для декораторов;
• Icon — генераторы.

Большая часть других возможностей Python (например, байт-компиляция исходного кода) также была реализована ранее в других языках.

Портируемость

Python портирован и работает почти на всех известных платформах — от КПК до мейнфреймов. Существуют порты под Microsoft Windows, практически все варианты UNIX (включая FreeBSD и Linux), Plan 9, Mac OS и Mac OS X, iPhone OS 2.0 и выше, Palm OS, OS/2, Amiga, HaikuOS, AS/400 и даже OS/390, Windows Mobile, Symbian и Android^[16].

По мере устаревания платформы её поддержка в основной ветви языка прекращается. Например, с серии 2.6 прекращена поддержка Windows 95, Windows 98 и Windows ME^[17]. Однако на этих платформах можно использовать предыдущие версии Python — на данный момент сообщество активно поддерживает версии Python начиная от 2.3 (для них выходят исправления).

При этом, в отличие от многих портируемых систем, для всех основных платформ Python имеет поддержку характерных для данной платформы технологий (например, Microsoft COM/DCOM). Более того, существует специальная версия Питона для виртуальной машины Java — Jython, что позволяет интерпретатору выполняться на любой системе, поддерживающей Java, при этом классы Java могут непосредственно использоваться из Питона и даже быть написанными на Питоне. Также несколько проектов обеспечивают интеграцию с платформой Microsoft .NET, основные из которых — IronPython и Python.Net.

Типы и структуры данных

Python поддерживает динамическую типизацию, то есть тип переменной определяется только во время исполнения. Поэтому вместо «присваивания значения переменной» лучше говорить о «связывании значения с некоторым именем». В Python имеются встроенные типы: булевый, строка, Unicode-строка, целое число произвольной точности, число с плавающей запятой, комплексное число и некоторые другие. Из коллекций в Python встроены: список, кортеж (неизменяемый список), словарь, множество и другие^[18]. Все значения являются объектами, в том числе функции, методы, модули, классы.

Добавить новый тип можно либо написав класс (class), либо определив новый тип в модуле расширения (например, написанном на языке C). Система классов поддерживает наследование (одиночное и множественное) и метапрограммирование. Возможно наследование от большинства встроенных типов и типов расширений.

Все объекты делятся на ссылочные и атомарные. К атомарным относятся int, long, complex и некоторые другие. При присваивании атомарных объектов копируется их значение, в то время как для ссылочных копируется только указатель на объект, таким образом, обе переменные после присваивания используют одно и то же значение. Ссылочные объекты бывают изменяемые и неизменяемые. Например, строки и кортежи являются неизменяемыми, а списки, словари и многие другие объекты — изменяемыми. Кортеж в Питоне является, по сути, неизменяемым списком. Во многих случаях кортежи работают быстрее списков^[19], поэтому если вы не планируете изменять последовательность, то лучше использовать именно их.

Синтаксис и семантика

Язык обладает чётким и последовательным синтаксисом, продуманной модульностью и масштабируемостью, благодаря чему исходный код написанных на Питоне программ легко читаем.

Операторы

Набор операторов достаточно традиционен. Вот некоторые из них:

• условный оператор if (если). Альтернативный блок после else (иначе). Если условий и альтернатив несколько, можно использовать elif (сокр. от else if).
• операторы цикла while (пока) и for (для). Внутри цикла возможно применение break и continue для прерывания цикла и перехода сразу к следующей итерации соответственно.
• оператор определения класса class.
• оператор определения функции, метода или генератора def. Внутри возможно применение return (возврат) для возврата из функции или метода, а в случае генератора — yield (давать).
• оператор обработки исключений try — except — else или try — finally (начиная с версии 2.5, можно использовать finally, except и else в одном блоке).
• оператор pass ничего не делает. Используется для пустых блоков кода.

Одной из интересных синтаксических особенностей языка является выделение блоков кода с помощью отступов (пробелов или табуляций), поэтому в Питоне отсутствуют операторные скобки begin/end, как в языке Паскаль, или фигурные скобки, как в Си. Такой «трюк» позволяет сократить количество строк и символов в программе и приучает к «хорошему» стилю программирования. С другой стороны, поведение и даже корректность программы может зависеть от начальных пробелов в тексте. Некоторым такое поведение может показаться неинтуитивным и неудобным.

Выражения

Выражение является полноправным оператором в Питоне. Состав, синтаксис, ассоциативность и приоритет операций достаточно привычны для языков программирования и призваны минимизировать употребление скобок.

Отдельно стоит упомянуть операцию форматирования для строк (работает по аналогии с printf() из Си), которая использует тот же символ, что и взятие остатка от деления:

>>> print ("Здравствуй, %s!" % "Мир")
Здравствуй, Мир!

Python имеет удобные цепочечные сравнения. Такие условия в программах — не редкость:

1 <= a < 10 and 1 <= b < 20