itertools.combinations代码分析，,def combinat

itertools.combinations代码分析，,def combinat

def combinations(iterable, r):    # combinations('ABCD', 2) --> AB AC AD BC BD CD    # combinations(range(4), 3) --> 012 013 023 123    pool = tuple(iterable)    n = len(pool)    if r > n:        return    indices = range(r)    yield tuple(pool[i] for i in indices)    while True:        for i in reversed(range(r)):            if indices[i] != i + n - r:                break        else:            return        indices[i] += 1        for j in range(i+1, r):            indices[j] = indices[j-1] + 1        yield tuple(pool[i] for i in indices)#该片段来自于http://byrx.net