What is __name__ == “__main__” in Python?

When and how the main method is executed in Python and what does it means?

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If you are new to Python, you might have noticed that it is possible to run a Python script with or without a main method. But now you be wondering why do we need it then.

In this story, I am going to explain what is the use of the main method and what happens when you define it.

What does the if __name__ == “__main__”: do?

Before executing the code, the Python interpreter reads the source file and defines a few special variables/global variables. If the python interpreter is running that module (the source file) as the main program, it sets the special __name__ variable to have a value “__main__”. If this file is being imported from another module, __name__ will be set to the module’s name. The module’s name is available as value to __name__ global variable.

A module is a file containing Python definitions and statements. The file name is the module name with the suffix .py appended.

When we execute a file as the command to the python interpreter,

python follow.py
print ("Executed")
if __name__ == "__main__":
 print ("Executed when invoked directly")
else:
 print ("Executed when imported")

• All of the code that is at indentation level 0 [Block 1] gets executed. Functions and classes that are defined are, well, defined, but none of their code runs.
• Here, as we executed script.py directly __name__ variable will be __main__. So, code in this if block[Block 2] will only run if that module is the entry point to your program.
• Thus, you can test whether your script is being run directly or being imported by something else by testing the __name__ variable.
• If the script is getting imported by some other module at that time __name__ will be module name.

Why Do we need it?

For example, we are developing a script that is designed to be used as a module:

# Python program to execute function directly
def my_function():
 print ("I am inside function")
# We can test function by calling it.
my_function()

Now if we want to use that module by importing we have to comment out our call. Rather than that approach best approach is to use the following code:

# Python program to use main for function call.
if __name__ == "__main__":
 my_function()
import myscript
myscript.my_function()

Advantages :

1. Every Python module has its __name__ defined and if this is ‘__main__’, it implies that the module is being run standalone by the user and we can do corresponding appropriate actions.
2. If you import this script as a module in another script, the __name__ is set to the name of the script/module.
3. Python files can act as either reusable modules or as standalone programs.
4. if __name__ == “main”: is used to execute some code only if the file was run directly, and not imported.

Final Thoughts

Well, hopefully now you know the use of __name__ == “__main__” in Python. I hope you find this article helpful and have learned some new things. Share this article with your Pythoneer Friends.

Happy Coding!