count sort

sort.py

def counting_sort(l, upper_bound):
    counts = [0] * (upper_bound + 1)
    ret = []
    # count how many times each number occurs
    for i in l:
        counts[i] += 1
    # fill in ret
    for i, count in enumerate(counts):
        for _ in range(count):
            ret.append(i)
    return ret