In Python, the if __name__ == “__main__” idiom is a guard statement that is used to determine whether the code in the block following it is being run as the main program or being imported as a module into another program.

When a Python script is run, the interpreter assigns the special variable __name__ the value “__main__”. Therefore, when the script is run directly, __name__ will be set to “__main__” and the code following the if __name__ == “__main__”: block will be executed. However, if the script is imported as a module into another script, the __name__ variable will be set to the name of the module, and the code following the if __name__ == “__main__”: block will not be executed.

This idiom is particularly useful for separating the execution of a script into two parts:

1. The part that will be executed when the script is run directly.
2. The part that will be executed when the script is imported as a module into another script.

This allows you to write a script that can function as both a standalone program and as a module that can be imported into another script, without the need to worry about the main code block being executed when the script is imported as a module.

For example, let’s say you have a script called my_script.py that contains a function called main(). You want to be able to run this script directly and have the main() function execute, but you also want to be able to import this script as a module into another script and use the main() function without it executing. To accomplish this, you would use the if __name__ == “__main__”: idiom as follows:

def main():
    print("This is the main function")

if __name__ == "__main__":
    main()

In this example, the main() function is defined, but it is not called until the if __name__ == “__main__” block is reached. When the script is run directly, the __name__ variable will be set to “__main__”, so the main() function will be called. However, if the script is imported as a module, the main() function will not be executed until you are not calling it into main script.