L4.9: More Examples of Functions

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Learning outcomes

• write small utility functions
• return processed values from lists and strings
• compose functions for cleaner code

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Example 1: maximum of two numbers

def maximum(a, b):
    if a > b:
        return a
    return b

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Example 2: count vowels

def count_vowels(text):
    count = 0
    for ch in text.lower():
        if ch in "aeiou":
            count += 1
    return count

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Example 3: sum of list

def list_sum(nums):
    total = 0
    for x in nums:
        total += x
    return total

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Example 4: factorial function

def factorial(n):
    if n < 0:
        return None
    fact = 1
    for i in range(1, n + 1):
        fact *= i
    return fact

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Multiple returns via tuple

def min_max(nums):
    return min(nums), max(nums)

lo, hi = min_max([3, 9, 1, 5])
print(lo, hi)

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Exam hints and traps

• use return for reusable function result
• returning None can be intentional for invalid case
• function may return tuple if multiple values are needed

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Quick practice

1. Write function to count even numbers in a list.
2. Write function to reverse a string.
3. Write function to return both sum and average of a list.