What does if __name__ == __main__ do in Python?

   February 25, 2023
What does if "__name__" == "__main__" do in Python?

Introduction

Most of us have come across the if __name__ == “__main__” in Python while doing a program or we specifically write this function while doing a program. So what does this function basically do?

Here, we are going to see why we are using this if __name__ == “__main__” statement in the programs and how it is used and makes the program meaningful.

What is the __name__ attribute?

The Python interpreter includes the __name__ attribute while we execute the python code as it comes by default. It is a special attribute and it is one of the important names in the given local scope.

Example

Give the command dir() on the python console

output

Here you can see the __name__ is being found in the listing of the special attributes in the dir() function that specifies the class name, current module, or the module from where it is invoked.

Understanding __name__ == “__main__”

Let us create two files of python file1module.py and file2module.py

In file1module.py write the following code

print("First file name is {}".format(__name__))

Output:

output

So what actually happened here is that before python executes the code it sets some special variable and __name__ is one of the special variables when it executes the python file directly it sets __name__ == “__main__” so we are getting the output as the main function.

Consider the next python file file2module.py

import file1module
print("Second file name is {}".format(__name__))

Output:

output

Now in the second file i.e file2module.py we have actually imported the module file1module hence we are importing the functionalities of that module in our file2module.py. Now you can see the difference between the outputs. The first file is not considered as the __main__ file as it no longer runs directly and it is being imported in the second file as a module here file2module.py is considered as the __main__ module.

Now, write the following code in file1module.py

print("This is statement will be executed always")
def main():
    print("First file name is {}".format(__name__))

if __name__== "__main__":
    main()

Output:

output

The output here is __main__ which is pretty common as we have applied the if condition allowing it to print the output defined in the main function().

In the file2module.py

import file1module
print("Second file name is {}".format(__name__))

Output:

output

Here we can see the output in the second file is the __main__ as the “file1module”  is imported in the file2module.py so it will not consider the file1module as the __main__. Hence it will consider the condition if __name__ == “__main__” for the file2module.py and execute accordingly.

Run a particular function from file1module.py

import file1module

file1module.main()
print("Second file name is {}".format(__name__))

Output:

output

In some cases, if we want to run a particular function defined in file1module.py we can run it by calling it by filename.name_of_the_function. Hence we can get the output with the defined function from the imported module in the current module.

Conclusion

Hence we have learned if __name__ == “__main__” do in Python that allows executing the code as the script if you run the program directly and not being imported as a module. Hence this is providing different behavior when we are importing it as the module.

Hope you like this piece of information. Please let us know if you want us to include any important information left out to share.

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Author: Ayush Purawr