functions.md

Python by Example: Functions

Functions let you reuse code and organize logic. Define them with def; parameters go in parentheses; use return to send a value back. Python doesn't require type declarations—you can add type hints for clarity. Default arguments let callers omit optional parameters.

What you'll learn:

• Defining functions with def
• Parameters and return
• Default argument values
• Functions can take different types (dynamic typing)

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


# Call the function
print(greet("Alice"))


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


print(add(2, 3))
print(add("hello", " world"))


# Default arguments
def power(base, exp=2):
    return base ** exp


print(power(3))
print(power(3, 3))

power(3) uses the default exp=2, so it returns 9. power(3, 3) overrides it and returns 27. The same add function works for numbers and strings because Python is dynamically typed.

To run this program:

$ python source/functions.py
Hello, Alice!
5
hello world
9
27

Tip: Keep functions focused—one clear purpose per function. Shorter functions are easier to test and reuse.

Try it: Write a function that takes a name and age, and returns a greeting that includes both.

Source: functions.py

Next: Multiple Return Values