Problem:list of elements, one is unique, others always in pairs, find unique

 

	def unique(arr):
	""" find unique element in array
	1. only one is unique
	2. all the others are in pairs
	>>> unique([1, 2, 3, 4, 5, 6, 5, 4, 3, 2, 1])
	6
	A XOR A = 0
	0 XOR A = A
	"""
	x = 0
	for i in arr:
	x ^= i
	return x

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 Handy itertools:

• powerset

  	import itertols as it
  	def powerset(iterable):
  	"""
  	powerset([1,2,3]) --> () (1,) (2,) (3,) (1,2) (1,3) (2,3) (1,2,3)
  	"""
  	s = list(iterable)
  	return it.chain.from_iterable(it.combinations(s, r) for r in range(len(s)+1))

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• all sublist from list

  	def sublists(iterable):
  	""" generate all of the sublist from *iterable*.
  	>>> [s for s in sublists('hi')]
  	[('h',), ('i',), ('h', 'i')]
  	>>> list(sublists([0, 1, 2]))
  	[(0,), (1,), (2,), (0, 1), (1, 2), (0, 1, 2)]
  	"""
  	# The length-1 sublist
  	seq = []
  	for item in iter(iterable):
  	seq.append(item)
  	yield (item,)
  	seq = tuple(seq)
  	item_count = len(seq)
  	# And the rest
  	for n in range(2, item_count + 1):
  	for i in range(item_count - n + 1):
  	yield seq[i : i + n]

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