python itertools 模块完全掌握(2)

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1. 全部

count(start=0, step=1)
repeat(elem [,n])
accumulate(p[, func])
chain(p, q, …)
chain.from_iterable([p, q, …])
compress(data, selectors)
dropwhile(pred, seq)
groupby(iterable[, keyfunc])
filterfalse(pred, seq)
islice(seq, [start,] stop [, step])
starmap(fun, seq)
tee(it, n=2)
takewhile(pred, seq)
zip_longest(p, q, …)
product(p, q, … [repeat=1])
permutations(p[, r])
combinations(p, r)
combinations_with_replacement(p, r)
本节主要介绍8-18,1-7见上一节内容

2. 详解

#!/usr/bin/env python# encoding: utf-8"""@python version: python3.6.1@author: XiangguoSun@contact: sunxiangguodut@qq.com@site: http://blog.csdn.net/github_36326955@software: PyCharm@file: suggest5.py@time: 5/2/2017 5:58 PM"""import itertools# ex2.5:groupby# groupby(iterable[, keyfunc]) --> sub-iterators grouped by value of keyfunc(v)"""for item in iterable， 我们看一下keyfunc(item)的返回值，将返回值相同的列为一组。name为每一组对应的返回值，group为该组的成员"""qs = [{'date' : 1},{'date' : 2}][(name, list(group)) for name, group in itertools.groupby(qs, lambda p:p['date'])]"""lambda函数的输入p是qs的item， 返回值是qs每一项的'date'属性值。按照这个进行分组。output:[(1, [{'date': 1}]), (2, [{'date': 2}])]"""a = ['aa', 'ab', 'abc', 'bcd', 'abcde']for i, k in itertools.groupby(a, len):    print(i, list(k))"""output:2 ['aa', 'ab']3 ['abc', 'bcd']5 ['abcde']"""# ex2.6: filterfalse# filterfalse(pred, seq) --> elements of seq where pred(elem) is Falsedef pred(x):    return x < 1for x in itertools.filterfalse(pred, [-1,0,2,1,-3,2]):    print(x,end=',')"""output:2,1,2"""# ex2.7: islice# islice(seq, [start,] stop [, step]) --> elements from#       seq[start:stop:step]for x in itertools.islice([0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10], 1, 8, 2):    print(x, end=',')"""output:1,3,5,7,"""# ex2.8: starmap# starmap(fun, seq) --> fun(*seq[0]), fun(*seq[1]), ...values = [(0, 5), (1, 6), (2, 7), (3, 8), (4, 9)]for i in itertools.starmap(lambda x, y: (x, y, x*y), values):    print('%d * %d = %d' % i)"""output:0 * 5 = 01 * 6 = 62 * 7 = 143 * 8 = 244 * 9 = 36"""# ex2.9: tee# tee(it, n=2) --> (it1, it2 , ... itn) splits one iterator into n"""tee(it,n)中，it为一个迭代器，通过tee操作，我们可以得到n个一样的迭代器："""for x in itertools.tee([1,2,3,4,5,6],3):    for i in x:        print(i,end=",")    print()"""output:1,2,3,4,5,6,1,2,3,4,5,6,1,2,3,4,5,6,"""# ex2.10:takewhile# takewhile(pred, seq) --> seq[0], seq[1], until pred failsdef pred(x):    return x < 1for x in itertools.takewhile(pred, [-1,-2,0,3,4,-1,2]):    print(x,end=",")"""output:-1,-2,0,"""# ex2.11:zip_longest# zip_longest(p, q, ...) --> (p[0], q[0]), (p[1], q[1]), ...for x in itertools.zip_longest([0,1,2,3],[4,5],[6,7]):    print(x, end=",")"""output:(0, 4, 6),(1, 5, 7),(2, None, None),(3, None, None),"""# ex3: Combinatoric generators:# ex3.1:product# product(p, q, ... [repeat=1]) --> cartesian productimport itertoolsa = (1, 2, 3)b = ('A', 'B', 'C')c = itertools.product(a,b,repeat=1)d = itertools.product(a,b,repeat=2)for elem in c:    print(elem, end=",")print()for e in d:     # 在c得到的基础上，进行笛卡尔乘积    print(e, end=",")"""output:(1, 'A'),(1, 'B'),(1, 'C'),(2, 'A'),(2, 'B'),(2, 'C'),(3, 'A'),(3, 'B'),(3, 'C'),(1, 'A', 1, 'A'),(1, 'A', 1, 'B'),(1, 'A', 1, 'C'),(1, 'A', 2, 'A'),(1, 'A', 2, 'B'),(1, 'A', 2, 'C'),(1, 'A', 3, 'A'),(1, 'A', 3, 'B'),(1, 'A', 3, 'C'),(1, 'B', 1, 'A'),(1, 'B', 1, 'B'),(1, 'B', 1, 'C'),(1, 'B', 2, 'A'),(1, 'B', 2, 'B'),(1, 'B', 2, 'C'),(1, 'B', 3, 'A'),(1, 'B', 3, 'B'),(1, 'B', 3, 'C'),(1, 'C', 1, 'A'),(1, 'C', 1, 'B'),(1, 'C', 1, 'C'),(1, 'C', 2, 'A'),(1, 'C', 2, 'B'),(1, 'C', 2, 'C'),(1, 'C', 3, 'A'),(1, 'C', 3, 'B'),(1, 'C', 3, 'C'),(2, 'A', 1, 'A'),(2, 'A', 1, 'B'),(2, 'A', 1, 'C'),..."""# ex3.2:permutations# permutations(p[, r])"""全排列创建一个迭代器，返回iterable中所有长度为r的项目序列，如果省略了r，那么序列的长度与iterable中的项目数量相同：返回p中任意取r个元素做排列的元组的迭代器"""p="abc"for x in itertools.permutations(p):    print(x)"""output:('a', 'b', 'c')('a', 'c', 'b')('b', 'a', 'c')('b', 'c', 'a')('c', 'a', 'b')('c', 'b', 'a')"""# ex3.3:combinations# combinations(p, r)"""组合，参加ex3.2"""p = "abcd"for x in itertools.combinations(p,2):   #相当于C(4,2)    print(x)"""output:('a', 'b')('a', 'c')('a', 'd')('b', 'c')('b', 'd')('c', 'd')"""# ex3.4:combinations_with_replacement# combinations_with_replacement(p, r)"""这也是组合，但是允许重负例如‘abc’中求C(3,2)在ex3.3中有ab,ac,bc在本立中则有：aa,ab,ac,bb,bc,cc"""p = "abc"for x in itertools.combinations_with_replacement(p,2):   #相当于C(4,2)    print(x)"""output:('a', 'a')('a', 'b')('a', 'c')('b', 'b')('b', 'c')('c', 'c')"""

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