itertools.combinations(iterable, r)

从可迭代对象iterable中选取r个单位进行组合，并返回一个生成元组的迭代器

定义

def combinations(iterable, r):# combinations('ABCD', 2) --> AB AC AD BC BD CD# combinations(range(4), 3) --> 012 013 023 123pool = tuple(iterable)n = len(pool)if r > n:returnindices = list(range(r))yield tuple(pool[i] for i in indices)while True:for i in reversed(range(r)):if indices[i] != i + n - r:breakelse:returnindices[i] += 1for j in range(i+1, r):indices[j] = indices[j-1] + 1yield tuple(pool[i] for i in indices)

举例：具体像这样

应用

枚举验证6174（python程序设计实验8）