When you start working with other people’s code you will run into the if __name__ == '__main__' function at the end of the Python code. What does it mean?
def main():
pass
if __name__ == '__main__':
main()
What this function do is to check whether you run the module (or script) directly, or if you import the module from another one.
What it says is this:
If you run the module directly, execute the function, if you import the module, don’t run it.
Let’s break it out.
Basics on how Python runs a file
Whenever the Python reads a script, it does two actions:
- it sets a few special variables like
__name__; - it executes the code found in the script.
What __name__ does When Running a Script
Let’s build a main_module.py file as an example.
The script will print the __name__ variable.
When I execute the code using python main_module.py in the Terminal, the script will return __main__.
What __name__ does When Importing a Script
Now, let’s see what happens when I try to import the module.
I created a import_main.py python script that the only purpose is to import main_module.py.
If you are not familiar with how import works, all it does is that it executes the script that you import.
When I run python import_main.py, it runs the print(__name__) function that we wrote in main_module.py.
This time, however, the Terminal returns the name of the imported module instead of __main__ as it did earlier.
Wrap-up: if __name__ == ‘__main__’
Coming back to the main_module.py, let’s make this clearer with a complete example.
def main():
print('The Main() Function Executed')
if __name__ == '__main__':
main()
else:
print('The main() function did not execute')
What the main_module.py will now do is that:
If I execute main_module.py, print The Main() Function Executed, else if I import main_module.py print The main() function did not execute.
Run the Main() Function From Import_main
Now, If you want, you could run any function available in the main_module.py from import_main.py.
This is it, if __name__ == '__main__' is useful to import a Module to use the functions inside of it, without running the script.
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