学习itertools模块记住这张表就OK了
参考：http://docs.python.org/2/library/itertools.html#module-itertools
Infinite Iterators:
| Iterator | Arguments | Results | Example |
|---|---|---|---|
| count() | start, [step] | start, start+step, start+2*step, ... | count(10) --> 10 11 12 13 14 ... |
| cycle() | p | p0, p1, ... plast, p0, p1, ... | cycle('ABCD') --> A B C D A B C D ... |
| repeat() | elem [,n] | elem, elem, elem, ... endlessly or up to n times | repeat(10, 3) --> 10 10 10 |
Iterators terminating on the shortest input sequence:
| Iterator | Arguments | Results | Example |
|---|---|---|---|
| chain() | p, q, ... | p0, p1, ... plast, q0, q1, ... | chain('ABC', 'DEF') --> A B C D E F |
| 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 |
| dropwhile() | pred, seq | seq[n], seq[n+1], starting when pred fails | dropwhile(lambda x: x<5, [1,4,6,4,1]) --> 6 41 |
| groupby() | iterable[, keyfunc] | sub-iterators grouped by value of keyfunc(v) | |
| ifilter() | pred, seq | elements of seq where pred(elem) is true | ifilter(lambda x: x%2, range(10)) --> 1 3 5 79 |
| ifilterfalse() | pred, seq | elements of seq where pred(elem) is false | ifilterfalse(lambda x: x%2, range(10)) --> 02 4 6 8 |
| islice() | seq, [start,] stop [, step] | elements from seq[start:stop:step] | islice('ABCDEFG', 2, None) --> C D E F G |
| imap() | func, p, q, ... | func(p0, q0), func(p1, q1), ... | imap(pow, (2,3,10), (5,2,3)) --> 32 9 1000 |
| starmap() | func, seq | func(*seq[0]), func(*seq[1]), ... | starmap(pow, [(2,5), (3,2), (10,3)]) --> 32 91000 |
| tee() | it, n | it1, it2, ... itn splits one iterator into n | |
| takewhile() | pred, seq | seq[0], seq[1], until pred fails | takewhile(lambda x: x<5, [1,4,6,4,1]) --> 1 4 |
| izip() | p, q, ... | (p[0], q[0]), (p[1], q[1]), ... | izip('ABCD', 'xy') --> Ax By |
| izip_longest() | p, q, ... | (p[0], q[0]), (p[1], q[1]), ... | izip_longest('ABCD', 'xy', fillvalue='-') -->Ax By C- D- |
Combinatoric generators:
| Iterator | Arguments | Results |
|---|---|---|
| product() | p, q, ... [repeat=1] | cartesian product, equivalent to a nested for-loop |
| permutations() | p[, r] | r-length tuples, all possible orderings, no repeated elements |
| combinations() | p, r | r-length tuples, in sorted order, no repeated elements |
| combinations_with_replacement() | p, r | r-length tuples, in sorted order, with repeated elements |
| product('ABCD', repeat=2) | AA AB AC AD BA BB BC BD CA CB CC CD DA DB DC DD | |
| permutations('ABCD', 2) | AB AC AD BA BC BD CA CB CD DA DB DC | |
| combinations('ABCD', 2) | AB AC AD BC BD CD | |
| combinations_with_replacement('ABCD', 2) | AA AB AC AD BB BC BD CC CD DD |