scala - Why doesn't this Python code for powerset work? -
i can't identify blatantly wrong except trying scala-type operations python.
def powerset(arr): if len(arr) == 0: return [] elif len(arr) > 1: return powerset(arr[1:])+[arr[0]] i consistently error:
return powerset(arr[1:])+[arr[0]]
typeerror: unsupported operand type(s) +: 'nonetype' , 'list'
if len(arr) == 1
nothing returned ...
just change
def powerset(arr): if len(arr)>0: return powerset(arr[1:])+[arr[0]] else: return [] here powerset function https://docs.python.org/2/library/itertools.html
def powerset(iterable): "powerset([1,2,3]) --> () (1,) (2,) (3,) (1,2) (1,3) (2,3) (1,2,3)" s = list(iterable) return chain.from_iterable(combinations(s, r) r in range(len(s)+1)) here powerset implementation uses less magic
def powerset(seq): """ returns subsets of set. generator. """ if len(seq) <= 1: yield seq yield [] else: item in powerset(seq[1:]): yield [seq[0]]+item yield item print list(powerset([1,2])) 
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