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[轉載] Python itertools模塊詳解

isl 要點 bcd tools pla tle select for 輸入

  原文在這裏,寫的很詳細,感謝原作者,以下摘錄要點。

itertools用於高效循環的叠代函數集合。

無限叠代器

1 叠代器         參數         結果                                                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

處理輸入序列叠代器

 1 叠代器          參數            結果                                        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-

組合生成器

1 叠代器          參數                        結果
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

[轉載] Python itertools模塊詳解