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:
IteratorArgumentsResultsExamplecount()
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:
IteratorArgumentsResultsExamplechain()
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:
IteratorArgumentsResultsproduct()
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