How do I understand the main function of Python?

Python Empire (ID:PYTHONDG)

Difficulty: Beginner

Demo Environment:
Os:ubuntu 16.04
python:3.6

We often see the following statement when writing Python code. It seems to be the Main function of Python. What does it mean exactly?

if __name__ = = ' __main__ ': print (' Hello World ')

First Python has two concepts, source files :

~/code_house/py_dev$ tree.├──file1.py├──file2.py└──p_main.py

The contents are:

py_main.py

Import File1import file2if __name__ = = ' __main__ ': print (file1) print (file2) print (file1.__name__) print (file2 . __name__) Print (__name__) #py_main

Both file1.py and file2.py are empty, and then look at the effect of the operation:

~/code_house/py_dev$ python3 p_main.py <module ' file1 ' from '/home/xinwen/code_house/py_dev/file1.py ' >< Module ' file2 ' from '/home/xinwen/code_house/py_dev/file2.py ' >file1file2__main__

You can see the import of the file printed results are no longer a file but module

Print (file1): <module ' file1 ' from '/home/xinwen/code_house/py_dev/file1.py ' >print (file2): <module ' file2 ' From '/home/xinwen/code_house/py_dev/file2.py ' >

This is the form in which the Python source file is loaded into memory, and it exists in the form of a Python module.

and the name of the **module * * is also the name of the Python source code file:

Print (file1.__name__) file1print (file2.__name__) file2

Typically, the module name in memory is the corresponding file name. But one situation is different, when the file is used as a startup file, or the first file that is executed, the name of the module in memory generated by the file is no longer its file name:

Print (__name__) #py_main__main__

Unity is main .

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How do I understand the main function of Python?