Functions II

CDS1010: Week 6

Wiedemann • Fall 2025

Functions as Contracts/Promises

• Write functions so the caller can focus on what it does, not how it does it
• Describe what it does in a docstring

def clean_name(raw):
    """
    Trim whitespace from the raw string and convert it to title case.
    """
    text = raw.strip()
    return text.title()

Multiple Returns and Unpacking

• A function can return more than one value, separated by a comma
• These returns can be unpacked into separate names when calling

def min_max(numbers):
    """Return the smallest and largest values from the list."""
    smallest = numbers[0]
    largest = numbers[0]
    for value in numbers:
        if value < smallest:
            smallest = value
        if value > largest:
            largest = value
    return smallest, largest

lo, hi = min_max([3, 9, 2, 7])
print(f"The smallest value is {lo} and the largest value is {hi}.")

Helper Functions

• A function can be called by another function
• A helper function is a small, specialized function that helps another function do its job
• Helper functions keep code organized and readable, and make it easier to extend

def compute_average(nums):
    """Return the arithmetic mean of a list of numbers."""
    total = 0
    for n in nums:
        total += n
    return total / len(nums)

def show_average(nums):
    """Print a message with the average of a list of numbers."""
    avg = compute_average(nums)  # helper function called
    print("Average:", avg)