Python 函数化编程

  • 2020 年 4 月 19 日
  • AI

python提供了itertools用于高效循环的迭代函数集合
本文将依据官方文档,原封不动抄过来,先记录下,有时间再润色。

1 无限迭代器

迭代器 参数 结果 例子
count start, [stop] start, start+step, start+2*step count(10) –> 10 11 12 13 14 15 ……
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 n times repeat(10, 3) -> 10, 10, 10

2 处理输入序列迭代器

迭代器 参数 结果 例子
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 4 1
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 7 9
ifilterfalse() pred, seq elements of seq where pred(elem) is False ifilterfalse(lambda x: x%2, range(10)) –> 0 2 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 9 1000
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-

3 组合生成器

迭代器 参数 结果 例子
product() p, q, … [repeat=1] cartesian product, equivalent to a nested for-loop product(‘ABCD’, repeat=2) AA AB AC AD BA BB BC BD CA CB CC CD DA DB DC DD
permutations() p[, r] r-length tuples, all possible orderings, no repeated elements permutations(‘ABCD’, 2) AB AC AD BA BC BD CA CB CD DA DB DC
combinations() p, r r-length tuples, in sorted order, no repeated elements combinations(‘ABCD’, 2) AB AC AD BC BD CD
combinations_with_replacement() p, r r-length tuples, in sorted order, with repeated elements combinations_with_replacement(‘ABCD’, 2) AA AB AC AD BB BC BD CC CD DD