How to Call the Main Function in Python?

In Python programming, we use the main function. In this tutorial, I will show you how to call the main function in Python, its syntax, and a few examples.

To call the main function in Python, you first define the function using def main():, followed by your desired code inside this function. To ensure the main function is executed when the script is run directly, include the conditional statement if __name__ == "__main__": and call main() within it. This structure ensures that the main function is only executed when the script is run as the main program, not when it is imported as a module.

Table of Contents

What is the Main Function in Python?

In Python, the main function serves as the entry point of a script. It is similar to the main function in other programming languages like C or Java. The main function is not a built-in function in Python but a convention used to indicate where the program should start executing.

Why Use the Main Function?

Using a main function in your Python script has several advantages:

Improved Readability: It helps in organizing your code better.
Reusability: You can reuse the functions defined in the script by importing them into other scripts without executing the main code block.
Testing and Debugging: It makes testing and debugging easier since you can control the execution flow.

Syntax of the Main Function

The syntax to define and call the main function in Python is straightforward. Here’s a basic example:

def main():
    print("Hello, World!")

if __name__ == "__main__":
    main()

In this example:

def main(): defines the main function.
if __name__ == "__main__": checks if the script is being run directly or being imported as a module. If the script is run directly, it calls the main() function.

Check out Python Functions vs Methods

Call the Main Function in Python

Now let me show how to call the main function in Python with different scenarios and examples.

Scenario 1: Basic Script Execution

When you run the script directly, the main function will be executed. Here’s a simple example:

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

if __name__ == "__main__":
    main()

When you run this script, it will print:

This is the main function.

Here is the exact output you can see in the screenshot below:

Scenario 2: Importing the Script as a Module

If you import the script containing the main function into another script, the main function will not execute unless explicitly called. For example, consider the script above saved as script.py. Now, create another script:

import script

script.main()  # Explicitly calling the main function

In this case, the main function from script.py will be called and executed.

Check out Python Function Naming Conventions

Scenario 3: Passing Arguments to the Main Function

You can also pass arguments to the main function in Python. This is particularly useful for command-line applications. Here’s an example:

import sys

def main(args):
    print(f"Arguments passed: {args}")

if __name__ == "__main__":
    main(sys.argv[1:])

When you run this script with arguments, for example, python script.py arg1 arg2, it will print:

Arguments passed: ['arg1', 'arg2']

You can see the exact output in the screenshot below:

Call the Main Function in Python example

Scenario 4: Using Main Function in Larger Projects

In larger projects, the main function can help in organizing the code better. Here’s an example of a more complex script:

def initialize():
    print("Initializing...")

def process_data():
    print("Processing data...")

def main():
    initialize()
    process_data()
    print("Main function executed.")

if __name__ == "__main__":
    main()

This structure helps separate different parts of the code, making it more maintainable and readable.

Here is the exact output in the screenshot below:

Conclusion

In this tutorial, I have explained how to call the main function in Python with different examples.