How to Loop Through Lists in Python for Beginners

def transform_data(numbers):
    """Basic transformation examples using lists and loops."""
    doubled = []
    for n in numbers:
        doubled.append(n * 2)
    return doubled


def filter_even(numbers):
    """Keep only even numbers using a loop and condition."""
    evens = []
    for n in numbers:
        if n % 2 == 0:
            evens.append(n)
    return evens


def sum_all(numbers):
    """Add up all numbers using a loop."""
    total = 0
    for n in numbers:
        total += n
    return total


def find_max(numbers):
    """Track the largest value in a loop."""
    largest = numbers[0]
    for n in numbers:
        if n > largest:
            largest = n
    return largest


if __name__ == "__main__":
    sample = [3, 7, 2, 9, 4]
    print("Original:", sample)
    print("Doubled:", transform_data(sample))
    print("Evens:", filter_even(sample))
    print("Sum:", sum_all(sample))
    print("Max:", find_max(sample))