[Python beginner] If __name__ == Move your hand to understand'__main__'.

what will you do

ʻIf \ _ \ _ name \ _ \ _ =='\ _ \ _ main \ _ \ _': ` I experienced how the output changes in 4steps + 2steps.

This time, I will show the behavior when executing .py indirectly with a tool such as "spyder" that is often used by beginners.

If you want to run "$ python XXX.py" directly in the terminal, please see the details from at the bottom of this article.

Practice

__name__

1. First, write a function that print ('Hello!') And save it as "hello.py".

Example 1_hello.Define py

#hello.py
def function():
    print('Hello!')

2 . Try importing "hello.py" with the next new .py

Example 2_hello.import py

import hello
hello.function()

#Output contents
#--------------------
# Hello!
#--------------------

↓ You can see that the function has been executed.

3 Edit \ .hello.py and try to output \ _ \ _ name \ _ \ _ together

Example 3_add name

#hello.py
def function():
    print('Hello!')
    print(' __name__Then, what is displayed..!? -->' ,  __name__)

4 . When I try to import again ...

Example 4_hello.Try running py

import hello
hello.function()

#Output contents
#--------------------
#Hello!
#__name__Then, what is displayed..!? --> hello
#--------------------

↓ In the \ _ \ _ name \ _ \ _ part, "hello" of "hello.py" was displayed!

Conclusion (What is \ _ \ _ name \ _ \ _)

It turns out that \ _ \ _ name \ _ \ _ contains the module name 'hello' of the imported module 'hello.py'.

__main__

Next, edit hello.py and add \ _ \ _ main \ _ \ _.

Example 1_Put "Sato" in the main.

#hello.py
def function(name):
    print('Hello!',name)
    print('By the way__name__The contents are-->',__name__)

if __name__ == '__main__':
    print('Is the function in main executed?..?',function('Sato'))

Try running hello.py.

Example 2_Display "Tanaka"

import hello
hello.function('Tanaka')
#Output contents
#--------------------
#Hello! Tanaka
#By the way__name__The contents are--> hello
#--------------------

↓ \ _ \ _ Name \ _ \ _ remained the module name 'hello' of the module 'hello.py'. Therefore, the contents of ʻif name =='main':` (prepared "Sato") were not executed even though it was in function ().

Conclusion (What is \ _ \ _ main \ _ \ _)

I found that by setting ʻif name =='main': `, the following \ _ \ _ main \ _ \ _ is not executed.

Summary

Write the part that should not be executed when imported under ʻif name =='main': `.

• It is executed when calling directly such as $ python hello.py.

reference [Python] if name == What is'main':?