Python Functions

Definition: A function is a named, reusable block of code. You define it once, then "call" it whenever you need it — which keeps code organised and avoids repetition.

Example 1 — define and call

def greet():
    print("Hello!")

greet()   # call it
greet()   # call again

Use def, a name, brackets, and a colon. The indented lines are the function body.

Example 2 — parameters (inputs)

def greet(name):
    print("Hello, " + name)

greet("Sam")
greet("Alex")

Example 3 — returning a value

return sends a result back so you can use it elsewhere:

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

result = add(3, 4)
print(result)
print(add(10, 20))

Example 4 — default values

def greet(name="friend"):
    print("Hi, " + name)

greet()          # Hi, friend
greet("Sam")     # Hi, Sam

Example 5 — a small useful function

def is_even(n):
    return n % 2 == 0

print(is_even(4))   # True
print(is_even(7))   # False

💡 Tip: a good function does one clear job and has a name that says what it does, like calculate_total or send_email.