Python Functions and Modules

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Functions and Modules in Python

Functions bundle code and make programs maintainable. A module is a Python file with functions, classes and constants that you can reuse in other programs.

Defining functions

Use def to define a function. Parameters can have default values, return sends a result back:

def greet(name, greeting="Hello"):
    return f"{greeting}, {name}!"

print(greet("World"))   # Hello, World!

Parameter types

Positional: order matters.
Keyword arguments: greet(name="World").
*args / **kwargs: arbitrary positional / keyword arguments.

Importing modules

import math, from datetime import datetime or import numpy as np. Your own modules are .py files imported by name.

Tips

Keep functions small (one job per function).
Use descriptive names instead of a, b.
if __name__ == "__main__": protects executable code from running on import.