Counting Sort Python (for positive numbers only)

countingSort.py

def counting_sort(a, mn, mx):
    mx = max(a) if mx > max(a) else mx
    count, result = [0] * (max(a) + 1), []
    i, j = 0, mn
    while i < len(a):
        count[a[i]] += 1
        i += 1
    while j <= mx:
        result += [j] * count[j]
        j += 1
    return result


a = [2, 9, 3, 8, 5, 43, 0, 1, 2]

print(counting_sort(a, 0, 22))

suggesting a different data-type to represent numbers including negative range
dictionary?