Как написать хелло ворлд на питоне

print("Hello world!")

print(3 + 4)
print(3 * 5)
print(3 ** 2)

name = input("Как Вас зовут? ")
print("Привет,", name)

Для вставки кода на Python в комментарий заключайте его в теги <pre><code class=»python3″>Ваш код</code></pre>

Prerequisite: Python Language Introduction, Python 3 basics
In this article, we will look into about Python introduction ,its syntax ,why it is used and How to print “Hello World” in Python.
Python is a popular programming language. Created by Guido van Rossum and published in 1991.
Python is used for following purpose:-
 1) Web development (server-side)
 2)Software development
 3)Mathematics
 4)System scripting
Some features of Python :-
1)Python runs on many platforms (Windows, Mac, Linux, Raspberry Pi, etc.).
2)Python has a simple syntax similar to English.
3)Python has a syntax that allows developers to write programs in fewer lines than other programming languages.
4)Python runs in an interpreter system. This means that as soon as you write your code, you can run it. This means prototyping is very fast.
5)Python can be treated as procedural, object-oriented, or functional.
 

Python syntax compared to other programming languages:-
1) Developed for readability, Python shares some similarities with the math-influenced English
2) Python uses newlines to complete commands, unlike other programming languages ​​that often use semicolons and parentheses.
3) Python relies on indentation with spaces to define scope. Similar to loop, function, and class scoping. Other programming languages ​​often use curly braces for this purpose.

Method 1: Using Print()

Here we will be using the python print() function for the same. The print() function in python is used to print python objects as strings as standard output.

The python print function has the following syntax:

Syntax: Print(“string”)

Where: String: This string will be “Hello world”

Implementation:

Output:

Hello World

Method 2: Using sys

In this method we are going to print string using the sys module, sys module in Python provides various functions and variables that are used to manipulate different parts of the Python runtime environment. It allows operating on the interpreter as it provides access to the variables and functions that interact strongly with the interpreter. 

sys.std.write() : stdout is used to display output directly to the screen console.

Syntax: sys.stdout.write(“String”)

Code:

Output:

Hello World

Printing “Hello World” is usually the first thing a developer does when starting with a new programming language.

In this article, we will see how to print “Hello World” in Python.

The simplest way to print Hello World in Python is to pass a string to the print() function. The next step is to assign the string “Hello World” to a variable and then pass the variable to the print() function. This message can also be printed by using the + operator to concatenate two variables where the value of the first variable is “Hello” and the value of the second variable is “World”.

And these are just some ways to do that…

Let’s get creative and explore other possible ways!

1. How Do You Print Hello World in Python?

To print a message in Python you use the print() function. This is a function that receives a string as input and prints its value on the screen.

Let me explain…

Create a file called hello_world.py and add the following line of code to the file:

print("Hello World")

Note: you can create this file in a text editor or even better in an IDE like Visual Studio Code.

To run your program you can use the following command:

python hello_world.py

[output]
Hello World

We have specified the python command followed by the name of our Python program.

The extension .py identifies a file that contains Python code.

Important: in this tutorial, we are using Python 3.8. Also, in the following examples, we will always update the file hello_world.py with new code and we will execute our program using the Python command above.

2. Printing Hello World Using a Variable

In the previous section, we printed “Hello World” directly using the print() function.

This time I want to show you that it’s possible to assign the string “Hello World” to a variable first. Then after doing that you can print the value of the variable using the print() function.

Note: a variable allows storing data to be used in your program (in this case the string “Hello World”).

message = "Hello World using a variable"
print(message)

[output]
Hello World using a variable

Using the assignment operator ( = ) we have assigned the value on the right side of the operator to the variable message on its left side.

3. Concatenate two Python Strings to Print Hello World

We can also print our message by doing the following:

• Store the word “Hello” in a variable called word1
• Store the word “World” in a variable called word2
• Concatenate the two variables using the + operator

word1 = "Hello"
word2 = "World"
print(word1 + " " + word2)

Confirm that the output is “Hello World”.

Notice that we have concatenated one space character ” ” after word1 and before word2 to have a space between the words “Hello” and “World”.

Let’s see what happens if we remove that space character:

print(word1 + word2)

[output]
HelloWorld

We have removed the space between the two words.

4. Use the String format() Method to Print Hello World

Using the + operator to concatenate strings can get confusing when you try to create very long strings that contain several variables.

A cleaner option is to use the string format() method.

word1 = "Hello"
word2 = "World"
print("{} {}".format(word1, word2))

The first and second sets of curly brackets {} are replaced respectively by the values of the variables word1 and word2.

Let’s confirm the output is correct:

Hello World

It is correct!

5. Using Python f-strings to Print Hello World

With Python 3.6 and later you can use an alternative approach to the string format() method: Python f-strings.

Here is how it works…

word1 = "Hello"
word2 = "World"
print(f"{word1} {word2} using f-strings")

[output]
Hello World using f-strings

Notice the f letter just before the double quote.

This format is easier to read compared to the previous one considering that the variables word1 and word2 are embedded directly in the string.

Remember f-strings as they will definitely be useful in other Python programs.

6. Using a List and the String join() Method

So far we have used only strings…

In this section, we will introduce another data type: the list.

A list is used to store multiple values in a single variable. Lists are delimited by square brackets.

Firstly let’s assign the strings “Hello” and “World” to two items in our list called words.

words = ["Hello", "World"]

Then generate the message you want to print using the string join() method.

message = " ".join(words)

The join() method concatenates elements in a list (in this case our two words) using as a separator the string the join() method is applied to (in this case a single space ” “).

The result is that the worlds “Hello” and “World” are concatenated and an empty character is added between them.

print(message)

[output]
Hello World

Makes sense?

7. Using a List of Characters and the String join() Method

Let’s use a similar approach to the one in the previous section with the only difference being that in our list we don’t have words.

In our Python list, we have the individual characters of the string “Hello World”.

This example shows you that a Python string is made of individual characters.

characters = ['H','e','l','l','o',' ','W','o','r','l','d']

Notice that I have also included one space character between the characters of the two words.

Using the string join() method and the print() function we will print our message.

message = "".join(characters)
print(message)

[output]
Hello World

Nice!

8. Using Dictionary Values to Print Hello World in Python

But wait, there’s more!

In this section and in the next one we will use a different Python data type: the dictionary.

Every item in a dictionary has a key and a value associated with that key. A dictionary is delimited by curly brackets.

Let’s create a dictionary called words…

words = {1: "Hello", 2: "World"}

Here is how you can read this dictionary:

• First item: key = 1 and value = “Hello”
• Second item: key = 2 and value = “World”

We can generate the string “Hello World” by passing the values of the dictionary to the string join() method.

To understand how this works let’s print first the value of words.values().

print(words.values())

[output]
dict_values(['Hello', 'World'])

The values of the dictionary are returned in a list that we can then pass to the string join() method.

message = " ".join(words.values())
print(message)

[output]
Hello World

Test it on your computer to make sure you understand this syntax.

9. Using Python Dictionary Keys to Print Hello World

Once again in this section, we will use a dictionary…

The difference compared to the previous example is that we will store the strings “Hello” and “World” in the keys of the dictionary instead of using the values.

Our dictionary becomes…

words = {"Hello": 1, "World": 2}

Let’s go through this dictionary:

• First item: key = “Hello” and value = 1
• Second item: key = “World” and value = 2

This time let’s see what we get back when we print the keys of the dictionary using words.keys().

print(words.keys())

[output]
dict_keys(['Hello', 'World'])

Once again we get back a list.

At this point, we can concatenate the strings in the list of keys using the string join() method.

message = " ".join(words.keys())
print(message)

Verify that your Python program prints the correct message.

How Do You Print Hello World 10 Times in Python?

One last thing before completing this tutorial…

In your program, you might need to print a specific string multiple times.

Let’s see how we can do that with the message “Hello World”.

print("Hello World"*10)

Very simple…

I have used the * operator followed by the number of repetitions next to the string I want to repeat.

And here is the output:

Hello WorldHello WorldHello WorldHello WorldHello WorldHello WorldHello WorldHello WorldHello WorldHello World

Conclusion

Well done for completing this tutorial!

And if this is one of your first Python tutorials congratulations!!

To recap, we have covered a few Python basics here:

• Variables
• Data types (strings, lists, and dictionaries)
• print() function
• + operator to concatenate strings
• string methods .format() and .join()
• f-strings

It can be quite a lot if you are just getting started with Python so you might have to go through this tutorial a few times to make all these concepts yours.

Bonus read: we have used lists a few times in this tutorial. Go through another tutorial that will show you how to work with Python lists.

Введение

Hello World!

Инструкция по запуску первой программы в Python

Убедитесь, что Python установлен и команда

python -V

Показывает версию Python, например

Python 3.9.1

Если вы работаете в
Linux,
UNIX
или
Bash в Windows
перейдите в свою домашнюю директорию

В Linux

cd ~

В Windows

cd /mnt/c/Users/username

Создайте директорию python

mkdir python

Перейдите в неё, создайте файл hello_world.py
и откройте его любым тестовым редактором

cd python
touch hello_world.py
vi hello_world.py

Вставьте туда следующий код

print("Hello World!")

Выполните

python hello_world.py

В терминале должно появиться сообщение

Hello World!

Больше деталей о запуске скриптов вы можете найти в следующем параграфе —

«Запуск Python скрипта»

и затем в

if __name__ == «__main__»:

Запуск скрипта

Чтобы запустить .py скрипт введите

python имя_файла.py

Результат такого запуска зависит от того, что указано после

if __name__ == «__main__»:

если это условие вообще есть

print(«Hello!»)

python sample.py

Hello!

Теперь то же самое но в функции

def say_hello():
print(«Hello!»)

python sample.py

Ничего не произошло потому что функцию никто не вызвал

Можно добавить вызов функции следующим образом

def say_hello():
print(«Hello!»)

say_hello()

python sample.py

Hello!

В этом случае функция будет вызываться всегда — как при запуске скрипта из терминала так и при импорте в другой модуль
настроить это поведение можно с помощью переменной __name__ а точнее — с помощью условия

if __name__ == «__main__»:

Отступы (indentation)

Демонстрация

Рассмотрим файл for_loop.py

for i in range(1,4):print(i)

python for_loop.py

1
2
3

Всё работает прекрасно. Обратите внимание, что выведены были только i от 1 до 3. 4 python не вывел.

Если написать код не в одну строку, а следующим образом

for i in range(1,4):
print(i)

то работать код не будет. Получится ошибка

File «/home/andrei/python/for_loop.py», line 2
print(i)
^
IndentationError: expected an indented block

Поэтому нужно поставить перед print пробел

for i in range(1,3):

print(i)

python for_loop.py

1
2
3

Вместо одного пробела можно поставить табуляцию, но лучше поставить два или четыре пробела подряд.

PEP8

— документ, в котором собраны рекомендации по написанию Python кода говорит:

Use 4 spaces per indentation level

САМОЕ ВАЖНОЕ: Нельзя смешивать в одном файле отступы в виде табуляций и в виде
пробелов. Выберите один стиль и придерживайтесь его.

Про то как правильно переносить слишком длинные строки можете прочитать

здесь

Арифметика

/ — деление. Результат — число с плавающей точкой

>>> 5 / 2

2.5

// — целочисленное деление. Результат — округлённое до целого числа частное.

>>> 5 // 2

2

% — остаток от деления. Результат — остаток от //

>>> 5 % 2

1

Печать спецсимволов HTML

for i in range(100001,125000):
print "<tr><td>&#",i,";</td><td>&#",i,";</td></tr>"

Ссылки

Psyco
Shedskin
PyPy

Cython
Jython
IronPython

IDLE

Синтаксис

Set в фигурных скобках. Элемент добавляется с помощью .add()

if __name__ == ‘__main__’

print(f"Имя первого модуля: {__name__}")

# Если не любите f-string напишите:
print("Имя первого модуля: {}".format(__name__))

Запустим его

python3 first_module.py

Имя первого модуля: __main__

Во втором запишем

import first_module

Запустим его

python3 second_module.py

Имя первого модуля: __first_module__

Теперь когда все ясно, можно добавить в наш код условие if __name__ == «__main__»

def say_hello():
print(«Hello!»)

def display_name():
print(f«Имя первого модуля: {__name__}»)

if __name__ == «__main__»:
say_hello()

Hello!

Или

def say_hello():
print(«Hello!»)

def display_name():
print(f«Имя первого модуля: {__name__}»)

if __name__ == «__main__»:
display_name()

Имя первого модуля: __main__

Суть в том, что теперь мы определяем что будет выполняться при вызове этого скрипта а что нет.

Пакеты Python в Linux

Узнать сколько всего python3 пакетов в репозитории

Ubuntu

apt-cache search python3 | wc -l

3472

Изучить их названия можно с помощью less

apt-cache search python3 | less

alembic — lightweight database migration tool for SQLAlchemy

brltty — Access software for a blind person using a braille display

debian-goodies — Small toolbox-style utilities for Debian systems

devscripts — scripts to make the life of a Debian Package maintainer easier

libcrack2-dev — pro-active password checker library — development files

…

Проверить, существует ли файл

hosts

#!/usr/bin/python3

import os.path

if os.path.exists("/etc/hosts"):
print("hosts file exists")
else:
print("no hosts file")

или

#!/usr/bin/python3

try:
f = open('/etc/hosts')
print("hosts file exists")
except FileNotFoundError:
print("no hosts file")

python3 check_hosts.py

hosts file exists

Shebang

Указывает на нужный интерпретатор. Примеры:

#!/usr/bin/env python

#!/home/andrei/.pyenv/shims/python

После написаний шебанга нужно сделать скрипт выполняемым файлом

chmod + x имя_скрипта.py

И теперь его можно запускать прямо из терминала

./имя_скрипта.py

Или

.имя_скрипта.py

Scopes

LEGB

Ссылки на Local уничтожаются после выполнения функции

def fetch_words(url):
«»»Fetch a list of words from a URL.

Args:
url: The URL of a UTF-8 text document.

Returns:
A list of strings containing the words from
the document
«»»
# PEP 257
# story = urlopen(«http://sixty-north.com/c/t.txt»)
story = urlopen(url)
story_words = []
for line in story:
line_words = line.decode(«utf8»).split()
for word in line_words:
story_words.append(word)
story.close()
return story_words

def print_items(story_words):
«»»Print items one per line.

Args:
An iterable series of printable items.
«»»
for word in story_words:
print(word)

def main(url):
words = fetch_words(url)
print_items(words)

if __name__ == «__main__»:
main(sys.argv[1])

Разберем поведение глобальных переменных

count = 0

def show_count():
print(count)

def set_count(c):
count = c

show_count() # 0
set_count(5)
show_count() # 0

0
0

Изменить поведение функции можно с помощью global

count = 0

def show_count():
print(count)

def set_count(c):
global count
count = c

show_count() # 0
set_count(5) # Now affects global variable
show_count() # 5

0
5

Полезные ссылки

«Hello World» на языке Python.

«Hello World» на языке программирования Python выглядит следующим образом:

print ('Привет, Python!')

Вы можете попробовать запустить ее, набрав текст в интерпретаторе Python3.

Более сложная программа «Hello World», с интерактивным вводом выглядит так:

name = input("Как тебя зовут? ")
print('Привет,' ,name)

Во время исполнения программы появляется сообщение:

> Как тебя зовут?

пишем имя, например Тёма и жмем клавишу Enter

После этого получаем вывод:

> Привет, Тёма