Functions

A function is a named, reusable block of code. Anywhere you find yourself writing similar code more than once, that's usually a sign it should be a function instead.

main.py

Try it yourself →

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

print(greet("Alice"))
print(greet("Bob"))

Output

Hello, Alice!
Hello, Bob!

def starts a function definition, followed by its name and parameters in parentheses
return sends a value back to wherever the function was called — without it, a function returns None
name is a parameter — a placeholder that gets filled in with whatever you pass when you call the function

Default arguments

You can give a parameter a default value, making it optional — callers can leave it out entirely, or override it when they need something different.

main.py

Try it yourself →

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

print(greet("Alice"))
print(greet("Bob", "Hi"))

Output

Hello, Alice!
Hi, Bob!

Next: lambda functions — small, throwaway functions written in a single line.

Practice exercise

Write a function square(n) that returns n * n, then print square(6).

← while Loops Lambda Functions →