我想找到一种干净巧妙的方法（在python中）来找到1s和0s x chars字符串的所有排列。理想情况下，这将是快速的，并且不需要进行太多的迭代…

因此，对于x = 1，我想要：[‘0’，‘1’] x = 2 [‘00’，‘01’，‘10’，‘11’]

等等..

现在我有这个，它很慢，看起来很不雅：

    self.nbits = n
    items = []
    for x in xrange(n+1):
        ones = x
        zeros = n-x
        item = []
        for i in xrange(ones):
            item.append(1)
        for i in xrange(zeros):
            item.append(0)
        items.append(item)
    perms = set()
    for item in items:
        for perm in itertools.permutations(item):
            perms.add(perm)
    perms = list(perms)
    perms.sort()
    self.to_bits = {}
    self.to_code = {}
    for x in enumerate(perms):
        self.to_bits[x[0]] = ''.join([str(y) for y in x[1]])
        self.to_code[''.join([str(y) for y in x[1]])] = x[0]