Python if __name__ == "__main__" Explanation

Find out what is if __name__ == “__main__” in Python and its purpose. Learn about the __name__ attribute and when its value is set to “__main__”.

Table of Contents

What is `if name == "main"`?

You might have seen the following line of code in numerous python programs.

if __name__ == "__main__"

But what is its purpose? Let’s find out.

It is simply an if statement having the condition __name__ == "__main__"

The condition is to check if the attribute __name__ has the string type value "__main__".

`name` Attribute and `"main"` value

Every module in python has some special attributes and __name__ is one of them. The value of this module is usually set to "__main__" or to contain the name of the current module.

Examples

Let’s understand this concept with the help of examples.

I’ve created a file named some_module.py and written the following code into it.

#some_module.py

def demo():
    print("This is a demo function of some_module.")
    
if __name__ == "__main__":
    print("The program is executed as the main program.")
    print("As you can see, the value of __name__ is", __name__)
    print("That's why the control is inside the if statement body.")
    print("Calling demo() Function")
    demo()

#some_module.py

def demo():

print("This is a demo function of some_module.")

if __name__ == "__main__":

print("The program is executed as the main program.")

print("As you can see, the value of __name__ is", __name__)

print("That's why the control is inside the if statement body.")

print("Calling demo() Function")

demo()

Now, to execute the python code written in the file, some_module.py, I used the following command.

python some_module.py

And it printed the following output to the console.

The program is executed as the main program.
As you can see, the value of __name__ is __main__
That's why the control is inside the if statement body.
Calling demo() Function
This is a demo function of some_module.

This code was simple. As the value of the attribute __name__ matches with the value __main__, therefore, every single statement that was written inside the if block is executed and hence the function demo() is also being called.

Now we’ve created a new file named try.py and inside this file, the following python code is written.

#try.py
import some_module

#Calling demo() function from some_module
some_module.demo()

print(__name__)
print(some_module.__name__)

#try.py

import some_module

#Calling demo() function from some_module

some_module.demo()

print(__name__)

print(some_module.__name__)

Now, clearly observe the output of the above code by running the try.py file using the following command.

python try.py

As you can see in the output, __name__ still has the value __main__ but we refer the __name__ attribute for some_module it gives the value some_module.

This is a demo function of some_module.
__main__
some_module

I hope now you have clear idea about the value of the __name__ attribute.

If it’s called within the module itself, it has the value __main__ while if it is called in some other module by the original module reference, its value is the name of the module itself.

Also, the if block code is now not executed as the value of the attribute __name__ is not anymore __main__.

I hope you found this guide useful. If so, do share it with others who are willing to learn Python. If you have any questions related to this article, feel free to ask us in the comments section.

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