Python: what if __name__ == “__main__” does?
In this article we’ll see in detail what if __name__ == “main” does, a statement we sometimes come across in libraries, for example.
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This instruction is sometimes found in third party libraries/code and seems a bit mysterious, what does it do?
Basically we can understand that when our code from one file is not imported into another __name__ will be __main__
When our foo.py file, for example, is imported into the bar.py file
The value of __name__ becomes bar.py, in the foo.py file
In bar the __name__ is still __main__, as it is the ‘main’ file
See the examples down below:
def printSomething(): print("Print only if __name__ is __main__") if(__name__ == "__main__"): printSomething() else: print("__name__ is not __main__")
In this case we will have the the following print:
Print only if __name__ is __main__
Because __name__ is __main__, it is the main file running
Now let’s see what happens if we import foo.py into this bar.py file:
import foo print("name in bar is: " + __name__)
We will have the following output if we run bar.py:
__name__ is not __main__
This is due to the fact explained above, the file foo was imported
So the name of __main__ is changed too
And the validation if __name__ == “__main__” is only True, when this file is not imported in others
In this article we learned what if __name__ == “main”: does and how we can use it
The idea is that the __name__ is only __main__ in your file, when it is not imported into others
If it’s imported, its __name__ will be the name of the file, when called by this other file it was imported into
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