Python Main function

1. Purpose of the Main Function

In Python, the “main function” is a conventional entry point that controls program execution flow.

def main():
    print("Program started")

main()

This provides a clear structure and separation of execution logic.

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2. Using if __name__ == "__main__"

def main():
    print("Main function executed")

if __name__ == "__main__":
    main()

This ensures the main logic runs only when the file is executed directly, not when imported.

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3. Why __name__ Works

print(__name__)

• When run directly → __main__

• When imported → module name

This enables safe reusability of scripts as modules.

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4. Main Function with Parameters

def main(name):
    print(f"Welcome, {name}")

if __name__ == "__main__":
    main("Alice")

The main function can accept arguments like any other function.

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5. Main Function for Program Flow Control

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

def main():
    print("Initializing system...")
    process_data()

if __name__ == "__main__":
    main()

The main function orchestrates program execution in a clean, readable order.

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6. Using Main with Command-Line Arguments

import sys

def main():
    print("Arguments received:", sys.argv)

if __name__ == "__main__":
    main()

Allows integration with command-line tools and automation workflows.

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7. Separating Business Logic from Entry Point

def calculate_total(a, b):
    return a + b

def main():
    result = calculate_total(10, 20)
    print("Total:", result)

if __name__ == "__main__":
    main()

Improves modularity and testability.

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8. Main Function in Large Applications

def initialize():
    print("System initialized")

def run():
    print("Application running")

def shutdown():
    print("System shutdown")

def main():
    initialize()
    run()
    shutdown()

if __name__ == "__main__":
    main()

Supports structured application life-cycle management.

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9. Main Function with Error Handling

def main():
    try:
        print("Executing task...")
    except Exception as e:
        print("Error occurred:", e)

if __name__ == "__main__":
    main()

Encapsulates exception handling at the entry level.

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10. Production-Ready Main Template

def main():
    """Application entry point"""
    print("Application started")

if __name__ == "__main__":
    main()

Standard best practice for scalable, maintainable Python applications.

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