Classes and Objects in Python- Object Oriented Programming & A Project

what is __Main__ module. what are saved here?

The __main__ module in Python refers to the module that serves as the entry point to your program when it is run directly. It is a special module name that Python assigns to the script that is executed in the context of the main program. Here’s what you should know about it:

Purpose of __main__

1. Entry Point: When you run a Python script directly using python script.py, Python sets the __name__ variable for that script to "__main__". This indicates that the script is being run as the main program.
2. Module Context:
   • Any code inside the script that is not within a function or class definition is executed when the script is run as __main__.
   • It provides a way to structure Python programs so that certain code only runs when the script is executed directly, not when it is imported as a module into another script.

What is Saved in __main__

• Global Variables: Variables defined at the top level of the script (not inside any function or class) are saved in the __main__ module.
• Function Definitions: Functions defined at the top level of the script are part of the __main__ module.
• Executable Code: Any executable code outside of function and class definitions is part of the __main__ module and executes when the script is run directly.

Example:

Consider a simple Python script example.py:

# example.py

def hello():
    return "Hello, World!"

print("This is executed in __main__")

if __name__ == "__main__":
    print("Running directly")
    result = hello()
    print(result)

• When you run python example.py:
  • "This is executed in __main__" and "Running directly" are printed because they are in the __main__ module.
  • The hello() function is called and its result "Hello, World!" is printed.
• If you import example.py as a module in another script:
  • The code inside if __name__ == "__main__": block does not execute.
  • You can still import and use the functions and variables defined in example.py.

The __main__ module in Python is where the code execution begins when a script is run directly. It includes global variables, function definitions, and executable code that are not within function or class definitions. Understanding __main__ helps you structure your Python programs to handle both standalone execution and module import scenarios effectively.