Built-in Variable __name__

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Built-in Variable __name__#

The Python variable __name__ is a special built-in variable that is a part of the Python runtime environment. Here’s what it represents:

  • When a Python script is executed, the interpreter reads the source file and defines a few special variables before executing the code. One of these special variables is __name__.

  • If the script is being run as the main program, the value of __name__ is set to '__main__'. This indicates that the script is not being imported from another module but is being executed directly.

  • Conversely, if the script is being imported into another module, name is set to the name of the script/module being imported.

This behavior of the __name__ variable is useful for determining whether a script is being run on its own or being used by another script as a module. It allows developers to control which parts of their code should be executed when the module is run directly and which parts should be executed when the module is imported. Bold the relevant parts of the response to improve readability.

Here’s what it does:

if __name__ == "__main__":
    main()

  • __name__ is a special built-in variable in Python that represents the name of the current module.

  • When a Python script is run directly (for example, python script.py from the command line), the __name__ variable is set to "__main__".

  • If the script is being imported into another module, __name__ will be set to the name of the script/module.

  • main() is typically a function that contains the code to be executed when the script is run directly. It’s not a built-in function but is often defined by the programmer to organize code.

So, the if statement checks: if this script is the main program being executed, then call the main() function and run the code inside it. This allows a script to provide functionality for other scripts to import, while also providing a standalone functionality when the script is executed on its own. It’s a way to make a Python file both reusable as a module and executable as a script. Bold the relevant parts of the response to improve readability.

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Demo Code#

Here’s a short Python program demonstrating the __name__ attribute:

Python

def greet(name):
  print(f"Hello, {name}!")

if __name__ == "__main__":
  greet("World")  # Call greet only when running as a script

print("This line is always executed")

Explanation:

  1. We define a function greet that takes a name and prints a greeting.

  2. The if __name__ == "__main__": block checks if the script is being run directly (as the main program) or imported as a module.

  3. Inside the if block, we call greet("World"). This ensures the greeting is printed only when the script is executed directly.

  4. Outside the if block, we print another message. This line will always be executed, regardless of whether the script is run directly or imported.

Running the program:

  • Save the code as a Python file (e.g., demo.py).

  • To run the script directly, open a terminal and navigate to the directory where you saved the file. Then, type:

Bash

python demo.py

This will print:

Hello, World!
This line is always executed

  • To import the script as a module, create another Python file and use the import statement:

Python

import demo

demo.greet("Friend")  # Call the greet function from the imported module

This will only print:

Hello, Friend!

The __name__ check ensures the greeting functionality is only executed when running the script directly, not when imported as a module.

In Short: It Allows You to Execute Code When the File Runs as a Script, but Not When It’s Imported as a Module

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