def butter(f, x):
    """prec: f is a function defined on the elements of x
    returns a list that if x f-ed.
    """
    out = []
    for k in x:
        out.append(f(k))
    return out
def better_butter(f, x):
    return [f(k) for k in x]
def trimmed_sum(x, limit):
    """prec: x is a numerical list, limit is a number
    postc: returns the sum of all elements of x <= limit.
    """
    total = 0
    for k in x:
        if k <= limit:
            total += k
    return total
def better_trimmed_sum(x, limit):
    return sum([k for k  in x if k <= limit])
            
print(butter(lambda x: x*x*x, [1,2,3,4]))
print(better_butter(lambda x: x*x*x, [1,2,3,4]))