[转载] Python itertools模块详解
原文在这里，写的很详细，感谢原作者，以下摘录要点。
itertools用于高效循环的迭代函数集合。
无限迭代器
1 迭代器 参数 结果 例子 2 count() start, [step] start, start+step, start+2*step, ... count(10) --> 10 11 12 13 14 ... 3 cycle() p p0, p1, ... plast, p0, p1, ... cycle('ABCD') --> A B C D A B C D ... 4 repeat() elem [,n] elem, elem, elem, ... endlessly or up to n times repeat(10, 3) --> 10 10 10
处理输入序列迭代器
1 迭代器 参数 结果 例子 2 chain() p, q, ... p0, p1, ... plast, q0, q1, ... chain('ABC', 'DEF') --> A B C D E F 3 compress() data, selectors (d[0] if s[0]), (d[1] if s[1]), ... compress('ABCDEF', [1,0,1,0,1,1]) --> A C E F 4 dropwhile() pred, seq seq[n], seq[n+1], starting when pred fails dropwhile(lambda x: x<5, [1,4,6,4,1]) --> 6 4 1 5 groupby() iterable[, keyfunc] sub-iterators grouped by value of keyfunc(v) 6 ifilter() pred, seq elements of seq where pred(elem) is True ifilter(lambda x: x%2, range(10)) --> 1 3 5 7 9 7 ifilterfalse() pred, seq elements of seq where pred(elem) is False ifilterfalse(lambda x: x%2, range(10)) --> 0 2 4 6 8 8 islice() seq, [start,] stop [, step] elements from seq[start:stop:step] islice('ABCDEFG', 2, None) --> C D E F G 9 imap() func, p, q, ... func(p0, q0), func(p1, q1), ... imap(pow, (2,3,10), (5,2,3)) --> 32 9 1000 10 starmap() func, seq func(*seq[0]), func(*seq[1]), ... starmap(pow, [(2,5), (3,2), (10,3)]) --> 32 9 1000 11 tee() it, n it1, it2 , ... itn splits one iterator into n 12 takewhile() pred, seq seq[0], seq[1], until pred fails takewhile(lambda x: x<5, [1,4,6,4,1]) --> 1 4 13 izip() p, q, ... (p[0], q[0]), (p[1], q[1]), ... izip('ABCD', 'xy') --> Ax By 14 izip_longest() p, q, ... (p[0], q[0]), (p[1], q[1]), ... izip_longest('ABCD', 'xy', fillvalue='-') --> Ax By C- D-
组合生成器
1 迭代器 参数 结果 2 product() p, q, ... [repeat=1] cartesian product, equivalent to a nested for-loop 3 permutations() p[, r] r-length tuples, all possible orderings, no repeated elements 4 combinations() p, r r-length tuples, in sorted order, no repeated elements 5 combinations_with_replacement() p, r r-length tuples, in sorted order, with repeated elements 6 product('ABCD', repeat=2) AA AB AC AD BA BB BC BD CA CB CC CD DA DB DC DD 7 permutations('ABCD', 2) AB AC AD BA BC BD CA CB CD DA DB DC 8 combinations('ABCD', 2) AB AC AD BC BD CD 9 combinations_with_replacement('ABCD', 2) AA AB AC AD BB BC BD CC CD DD
