Subset function

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I am new to Sage and trying to define a recursive function that returns the subsets for a given set. I get some sort of memory error for even the smallest sets and I don't know why:

def MySubsets(L):
    if L == []:
        return [[]]

    TheSubsets = MySubsets(L[1:len(L)])

    for subset in TheSubsets:
        newSubset = copy(subset)
        newSubset.append(L[0])

        TheSubsets.append(newSubset)

    return TheSubsets

...and while MySubsets([]) works, MySubsets([1]) already yields a memory error.