Python 给定列表中项目的组合

我现在在蟒蛇之地。这就是我需要做的。我已经查看了itertools库，但它似乎只进行排列

我想获取一个输入列表，比如['yahoo'、'wikipedia'、'freebase']，并生成一个项目与零个或多个其他项目的每个唯一组合

['yahoo', 'wikipedia', 'freebase']
['yahoo', 'wikipedia']
['yahoo', 'freebase']
['wikipedia', 'freebase']
['yahoo']
['freebase']
['wikipedia']

一些注释。顺序并不重要，我正在尝试设计一种方法来获取任意大小的列表。还有，这种组合有名字吗

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谢谢你的帮助

这称为功率集。照这个做就行了。下面是一个简单的实现：

def powerset(seq):
  if len(seq):
    head = powerset(seq[:-1])
    return head + [item + [seq[-1]] for item in head]
  else:
    return [[]]

>>> powerset(['yahoo', 'wikipedia', 'freebase'])
[[], ['yahoo'], ['wikipedia'], ['yahoo', 'wikipedia'], ['freebase'], ['yahoo', 'freebase'], ['wikipedia', 'freebase'], ['yahoo', 'wikipedia', 'freebase']]

还有一个：

def powerset(s):
  sets = []
  indicator = lambda x: x & 1
  for element in xrange(2**len(s)):
    n = element
    subset = []
    for x in s:
        if indicator(n):
            subset.append(x)
        n >>= 1
    sets.append(subset)
  return sets

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还有，为什么这个wiki？

你基本上是在用二进制从1数到2n-1：

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这叫做动力装置。这是从以下方面实施的：

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解决这个问题的有趣方法。我绝对不会这样想。

>>> l = ['yahoo', 'wikipedia', 'freebase']
>>> import itertools
>>> for i in range(1, len(l) +1):
    print(list(itertools.combinations(l, r=i)))


[('yahoo',), ('wikipedia',), ('freebase',)]
[('yahoo', 'wikipedia'), ('yahoo', 'freebase'), ('wikipedia', 'freebase')]
[('yahoo', 'wikipedia', 'freebase')]

0 0 1    ['freebase']
0 1 0    ['wikipedia']
0 1 1    ['wikipedia', 'freebase']
1 0 0    ['yahoo']
1 0 1    ['yahoo', 'freebase']
1 1 0    ['yahoo', 'wikipedia']
1 1 1    ['yahoo', 'wikipedia', 'freebase']

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) for r in range(len(s)+1))