def evens(input):
    """
    Returns a list with only the even elements of data

    Example: evens([0, 1, 2, 3, 4]) returns [0,2,4]

    Parameter input: The data to process
    Precondition: input an iterable, each element an int
    """
    result = []
    for x in input:
        if x % 2 == 0:
            result.append(x)
    return result