Python-based python if __name__ = = ' __main__ ': parsing

When you open a. py file, you will often see if __name__ = = ' __main__ ' at the bottom of the code: Now let's introduce its role.

The module is an object, and all modules have a built-in property of __name__. The value of the __name__ of a module depends on how you apply the module. If you import a module, the value of the module __name__ is usually the module file name, without the path or file extension. But you can also run the module directly like a standard program, in which case the __name__ value will be a special default "__main__".

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Run the. py file directly in cmd, then the value of __name__ is ' __main__ ';

After import a. py file, the value of __name__ is not ' __main__ ';

Thus use if __name__ = = ' __main__ ' to determine whether the. py file is running directly

Such as:

#Test. py

Class Test:

def __init (self):p

def f (self):p rint ' Hello, world! '

if __name__ = = ' __main__ ':

Test (). F ()

#End

You enter in cmd:

C:>python test.py

Hello, world!.

Description: "__name__ = = ' __main__ '" is established

You type in cmd again:

C:>python

>>>import Test

>>>test.__name__ #Test模块的__name__

' Test '

>>>__name__ #当前程序的__name__

' __main__ '

No matter what, test.py in the "__name__ = = ' __main__ '" will not be set up!

So, the next line of code will never run to!

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Python-based python if __name__ = = ' __main__ ': parsing