All uniques subsets of a set with duplicate elements

subsets.py

def subsets(a):
    result = [[]]
    a = sorted(a)
    i = 0
    while i < len(a):
        duplicates = 1
        while i < len(a) - 1 and a[i] == a[i + 1]:
            i += 1
            duplicates += 1
        size = len(result)
        for j in range(size):
            s = result[j].copy()
            for k in range(duplicates):
                s += [a[i]]
                result += [s.copy()]
        i += 1
    return result


print(subsets([1, 2, 2]))