Parsing of IF _ name _ = '_ main _' in Python

When you open a. py fileCodeAt the bottom of the page, we can see if _ name _ = '_ main _':. Now let's introduce its role.

A module is an object, and all modules have a built-in attribute _ name __. The value of _ name _ of a module depends on how you apply the module. If you import a module, the value of module _ name _ is usually the module file name, without the path or file extension. But you can also be like a standardProgramIn this case, the value of _ name _ is a special default value "_ main __".

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Run the. py file directly in cmd, and the value of _ name _ is '_ main __';

After importing a. py file, the value of __name _ Is Not '_ main;

Therefore, if _ name _ = '_ main _' is used to determine whether the. py file is directly running.

For example:

# Test. py

Class test:

Def _ Init (Self): Pass

Def F (Self): Print 'hello, world! '

If _ name _ = '_ main __':

Test (). F ()

# End

 

In cmd, enter:

C:> Python test. py

Hello, world!

Note: "_ name _ = '_ main _'" is true.

 

In cmd, enter:

C:> Python

>>> Import Test

>>> Test. _ name _ # test module's _ name __

'Test'

>>>__ Name _ # current program's _ name __

'_ Main __'

In any case, "_ name _ = '_ main _'" In test. py will not be true!

Therefore, the next line of code will never run!

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