itertools模块速查

2019-11-14 17:52:27

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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`

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