Function Examples¶

These examples reinforce the concepts from the previous sections: parameters, return values, type hints, and composition.

Square¶

A function with a single parameter and a return value.

def square(x: int) -> int:
    return x * x

print(square(5))

Output

Rectangle Area¶

A function with multiple parameters.

def area(length: float, width: float) -> float:
    return length * width

print(area(3.0, 4.0))

Output

12.0

Format Name¶

Functions work with any data type, not just numbers.

def format_name(first: str, last: str) -> str:
    return last.upper() + ", " + first

print(format_name("Alice", "Smith"))
print(format_name("Bob", "Lee"))

Output

SMITH, Alice
LEE, Bob

Temperature Conversion¶

A function that performs a real calculation.

def celsius_to_fahrenheit(c: float) -> float:
    return (c * 9 / 5) + 32

print(celsius_to_fahrenheit(25))

Output

77.0

Maximum Value¶

Functions can include conditional logic.

def max_value(a: int, b: int) -> int:
    if a > b:
        return a
    return b

print(max_value(10, 4))

Output

Composition¶

Functions can be combined by passing the return value of one function as the argument to another.

def square(x: int) -> int:
    return x * x

def double(x: int) -> int:
    return 2 * x

print(double(square(3)))

square(3) runs first and returns 9. That value is then passed to double, which returns 18.

Output

Key Ideas¶

This page concludes the functions section. A function is a black box that optionally takes inputs and optionally produces an output. Parameters let a function accept different values each time it is called, and the return statement sends a result back to the caller. Type hints document the expected types without changing how Python runs the code. Small functions can be composed — the return value of one becomes the argument of another — to build larger programs from simple, reusable pieces.

Next: Runtime Model (Call Stack).