iterstools很强大,务必要掌握https://docs.python.org/3/library/itertools.html
无限迭代器
迭代器参数结果例count()start, [step]start, start+step, start+2*step, ...count(10) --> 10 11 12 13 14 ...cycle()pp0, p1, ... plast, p0, p1, ...cycle('ABCD') --> A B C D A B C D ...repeat()elem [,n]elem，elem，elem，...无休止或多达n次repeat(10, 3) --> 10 10 10处理输入序列迭代器
迭代器参数结果例accumulate()p [,func]p0, p0+p1, p0+p1+p2, ...accumulate([1,2,3,4,5]) --> 1 3 6 10 15chain()p, q, ...p0, p1, ... plast, q0, q1, ...chain('ABC', 'DEF') --> A B C D E Fchain.from_iterable()可迭代p0, p1, ... plast, q0, q1, ...chain.from_iterable(['ABC', 'DEF']) --> A B C D E Fcompress()数据，选择器(d[0] if s[0]), (d[1] if s[1]), ...compress('ABCDEF', [1,0,1,0,1,1]) --> A C E Fdropwhile()pred, seqseq[n]，seq[n+1]，当pred失败时开始dropwhile(lambda x: x<5, [1,4,6,4,1]) --> 6 4 1filterfalse()pred, seqpred(elem)为false的seq的元素filterfalse(lambda x: x%2, range(10)) --> 0 2 4 6 8groupby()iterable[, keyfunc]通过keyfunc(v)的值分组的子迭代器---islice()seq, [start,] stop [, step]元素从seq[start:stop:step]islice('ABCDEFG', 2, None) --> C D E F Gstarmap()功能报func(seq[0]), func(seq[1]), ...starmap(pow, [(2,5), (3,2), (10,3)]) --> 32 9 1000takewhile()pred, seqseq[0]，seq[1]，直到pred失败takewhile(lambda x: x<5, [1,4,6,4,1]) --> 1 4tee()it，nit1，it2，... itn将一个迭代器拆分为n---zip_longest()p, q, ...(p[0], q[0]), (p[1], q[1]), ...zip_longest('ABCD', 'xy', fillvalue='-') --> Ax By C- D-组合生成器
迭代器参数结果product()p, q, ... [repeat=1]笛卡尔积，相当于嵌套for循环permutations()p[, r]r长度元组，所有可能的顺序，没有重复的元素combinations()p, rr长度元组，按排序顺序，没有重复的元素combinations_with_replacement()p, rr长度元组，按排序顺序，具有重复的元素product('ABCD', repeat=2)---AA AB AC AD BA BB BC BD CA CB CC CD DA DB DC DDpermutations('ABCD', 2)---AB AC AD BA BC BD CA CB CD DA DB DCcombinations('ABCD', 2)---AB AC AD BC BD CDcombinations_with_replacement('ABCD', 2)---AA AB AC AD BB BC BD CC CD DD2.1 itertools.count(start=0, step=1)
创建一个迭代器，生成从start开始的连续的数，start默认为0，step默认为1源代码 def count(start=0, step=1): # count(10) --> 10 11 12 13 14 ... # count(2.5, 0.5) -> 2.5 3.0 3.5 ... n = start while True: yield n n += step 使用 from itertools import * for i in zip(count(1),['a','b','c']): print(i) (1, 'a') (2, 'b') (3, 'c')2.2 itertools.cycle(iterable)
创建一个迭代器，对iterable中的元素遍历输出一次，内部会生成iterable中的元素的一个副本，反复循环该副本。源代码 def cycle(iterable): # cycle('ABCD') --> A B C D A B C D A B C D ... saved = [] # 遍历一次生成器 for element in iterable: yield element saved.append(element) # 反复执行副本 while saved: for element in saved: yield element 使用 from itertools import * i = 0 for item in cycle(['a', 'b', 'c']): i += 1 if i == 7: break print (i, item) 1 a 2 b 3 c 4 a 5 b 6 c2.3 itertools.repeat(object[, times])
创建一个迭代器，重复生成object，times（如果已提供）指定重复计数，如果未提供times，将无止尽返回该对象。源代码 def repeat(object, times=None): # repeat(10, 3) --> 10 10 10 # 如果times=None，无限循环 if times is None: while True: yield object else: for i in range(times): yield object 使用 from itertools import * for i in repeat('sweet_honey', 3): print (i) sweet_honey sweet_honey sweet_honey3.1 itertools.accumulate(iterable[, func])
创建一个迭代器，返回函数指定的操作方式，默认为累加和。源代码 import operator def accumulate(iterable, func=operator.add): 'Return running totals' # accumulate([1,2,3,4,5]) --> 1 3 6 10 15 # accumulate([1,2,3,4,5], operator.mul) --> 1 2 6 24 120 # 生成一个迭代器 it = iter(iterable) try: # 获取下一个值 total = next(it) # 遇到StopIteration，就返回空 except StopIteration: return # 如果没有报错，就返回total yield total # 从2开始累加 for element in it: total = func(total, element) yield total 使用 from itertools import accumulate import operator print(list(accumulate(range(10)))) [0, 1, 3, 6, 10, 15, 21, 28, 36, 45] print(list(accumulate(range(1,5), func = operator.mul))) [1, 2, 6, 24] print(list(list(accumulate(range(5,1,-1), max)))) [5, 5, 5, 5]3.2 itertools.chain(*iterables)
将几个可迭代的容器依次迭代源代码 def chain(*iterables): # chain('ABC', 'DEF') --> A B C D E F for it in iterables: for element in it: yield element 使用 from itertools import * for i in chain([1, 2, 3], ['a', 'b', 'c']): print (i) 1 2 3 a b c3.3 chain.from_iterable()
将可迭代容器里面的元素再次进行迭代一次源代码 def from_iterable(iterables): # chain.from_iterable(['ABC', 'DEF']) --> A B C D E F for it in iterables: for element in it: yield element 使用 from itertools import * for i in chain([['abc', 'bca','cba'],'abcd']): print(i) ['abc', 'bca', 'cba'] abcd for i in chain.from_iterable([['abc', 'bca','cba'],'abcd']): print(i) abc bca cba a b c d3.4 itertools.compress(data, selectors)
两个参数分别为data, selectors, 根据selectors中的真假情况返回data中的元素源代码 def compress(data, selectors): # compress('ABCDEF', [1,0,1,0,1,1]) --> A C E F return (d for d, s in zip(data, selectors) if s) 使用 from itertools import * for i in compress('ABCDEF', [1,0,1,0,1,1]) : print(i) A C E F3.5 itertools.dropwhile(predicate, iterable)
当predicate返回True时，跳过元素。一旦函数返回False，则开始收集剩下的所有元素到循环器源代码 def dropwhile(predicate, iterable): # dropwhile(lambda x: x<5, [1,4,6,4,1]) --> 6 4 1 iterable = iter(iterable) # 一直在找false for x in iterable: if not predicate(x): yield x break # 找到false 跳出上面的循环，进入这个循环直到结束 for x in iterable: yield x 使用 from itertools import * for i in dropwhile(lambda x: x<5, [1,4,6,4,1]) : print(i) 6 4 13.6 itertools.filterfalse(predicate, iterable)
当predicate返回False时，才将iterable中的元素添加进循环器源代码 def filterfalse(predicate, iterable): # filterfalse(lambda x: x%2, range(10)) --> 0 2 4 6 8 if predicate is None: predicate = bool for x in iterable: if not predicate(x): yield x 使用 from itertools import * for i in filterfalse(lambda x: x<5, [1,4,6,4,1]) : print(i) 63.7 itertools.groupby(iterable[, key])
将key的结果作用于iterable中的元素，将拥有相同返回结果的元素加入到循环器中，该函数之前需要确保iterable是经过排序的源代码 class groupby: # [k for k, g in groupby('AAAABBBCCDAABBB')] --> A B C D A B # [list(g) for k, g in groupby('AAAABBBCCD')] --> AAAA BBB CC D def __init__(self, iterable, key=None): if key is None: key = lambda x: x self.keyfunc = key self.it = iter(iterable) self.tgtkey = self.currkey = self.currvalue = object() def __iter__(self): return self def __next__(self): while self.currkey == self.tgtkey: self.currvalue = next(self.it) # Exit on StopIteration self.currkey = self.keyfunc(self.currvalue) self.tgtkey = self.currkey return (self.currkey, self._grouper(self.tgtkey)) def _grouper(self, tgtkey): while self.currkey == tgtkey: yield self.currvalue try: self.currvalue = next(self.it) except StopIteration: return self.currkey = self.keyfunc(self.currvalue) 使用 from itertools import * def height_classify(h): if h > 180: return 'tall' elif h < 160: return 'short' else: return 'middle' friends = [192, 158, 168, 195, 185, 170, 135, 174, 182] friends = sorted(friends, key=height_classify) for m, n in groupby(friends, key=height_classify): print(m) print(list(n)) middle [168, 170, 174] short [158, 135] tall [192, 195, 185, 182]3.7 itertools.islice(iterable, stop)
根据索引来选取迭代器的项源代码 def islice(iterable, *args): # islice('ABCDEFG', 2) --> A B # islice('ABCDEFG', 2, 4) --> C D # islice('ABCDEFG', 2, None) --> C D E F G # islice('ABCDEFG', 0, None, 2) --> A C E G s = slice(*args) it = iter(xrange(s.start or 0, s.stop or sys.maxint, s.step or 1)) nexti = next(it) for i, element in enumerate(iterable): if i == nexti: yield element nexti = next(it) 使用 from itertools import * for i in islice(count(), 5, 10): print (i, end=' ') 5 6 7 8 9 for i in islice(count(), 0, 100, 10): print (i, end=' ') 0 10 20 30 40 50 60 70 80 903.8 itertools.starmap(function, iterable)
用iterable 里面的项，构造function函数 def starmap(function, iterable): # starmap(pow, [(2,5), (3,2), (10,3)]) --> 32 9 1000 for args in iterable: yield function(*args) 使用 from itertools import * values = [(0, 5), (1, 6), (2, 7), (3, 8), (4, 9)] for i in starmap(lambda x,y:(x, y, x*y), values): print ('%d * %d = %d' % i) 0 * 5 = 0 1 * 6 = 6 2 * 7 = 14 3 * 8 = 24 4 * 9 = 363.9 itertools.takewhile(predicate, iterable)
和dropwhile相反，当predicate返回False时，跳过元素。一旦函数返回True，则开始收集剩下的所有元素到循环器源代码 def takewhile(predicate, iterable): # takewhile(lambda x: x<5, [1,4,6,4,1]) --> 1 4 for x in iterable: if predicate(x): yield x else: break 使用 from itertools import * for i in takewhile(lambda x: x<5, [1,4,6,4,1]) : print(i) 1 4 for i in dropwhile(lambda x: x<5, [1,4,6,4,1]) : print(i) 6 4 13.10 itertools.tee(iterable[, n=2])
从单个的iterable返回n个独立的循环器源代码 def tee(iterable, n=2): it = iter(iterable) deques = [collections.deque() for i in range(n)] def gen(mydeque): while True: if not mydeque: # when the local deque is empty newval = next(it) # fetch a new value and for d in deques: # load it to all the deques d.append(newval) yield mydeque.popleft() return tuple(gen(d) for d in deques) 使用 from itertools import * for i in tee([['abc', 'bca','cba'],'abcd']): for j in i: print(j) ['abc', 'bca', 'cba'] abcd ['abc', 'bca', 'cba'] abcd3.11 itertools.zip_longest(*iterables, fillvalue=None)
创建一个迭代器，聚合来自每个迭代器的元素。如果迭代的长度不均匀，那么缺失值将用 fillvalue 填充。迭代继续，直到最长可迭代被耗尽。源代码 class ZipExhausted(Exception): pass def zip_longest(*args, **kwds): # zip_longest('ABCD', 'xy', fillvalue='-') --> Ax By C- D- fillvalue = kwds.get('fillvalue') counter = len(args) - 1 def sentinel(): nonlocal counter if not counter: raise ZipExhausted counter -= 1 yield fillvalue fillers = repeat(fillvalue) iterators = [chain(it, sentinel(), fillers) for it in args] try: while iterators: yield tuple(map(next, iterators)) except ZipExhausted: pass 使用 from itertools import * for i in zip_longest('abcd','123',fillvalue='*'): print(i) ('a', '1') ('b', '2') ('c', '3') ('d', '*')4.1 itertools.product(*iterables, repeat=1)
笛卡尔乘积源代码 def product(*args, repeat=1): # product('ABCD', 'xy') --> Ax Ay Bx By Cx Cy Dx Dy # product(range(2), repeat=3) --> 000 001 010 011 100 101 110 111 pools = [tuple(pool) for pool in args] * repeat result = [[]] for pool in pools: result = [x+[y] for x in result for y in pool] for prod in result: yield tuple(prod) 使用 from itertools import * for i in product('abc','xy'): print(i) ('a', 'x') ('a', 'y') ('b', 'x') ('b', 'y') ('c', 'x') ('c', 'y')4.2 itertools.permutations(iterable, r=None)
全排列源代码 def permutations(iterable, r=None): # permutations('ABCD', 2) --> AB AC AD BA BC BD CA CB CD DA DB DC # permutations(range(3)) --> 012 021 102 120 201 210 pool = tuple(iterable) n = len(pool) r = n if r is None else r if r > n: return indices = list(range(n)) cycles = list(range(n, n-r, -1)) yield tuple(pool[i] for i in indices[:r]) while n: for i in reversed(range(r)): cycles[i] -= 1 if cycles[i] == 0: indices[i:] = indices[i+1:] + indices[i:i+1] cycles[i] = n - i else: j = cycles[i] indices[i], indices[-j] = indices[-j], indices[i] yield tuple(pool[i] for i in indices[:r]) break else: return 使用 from itertools import * for i in permutations('abcd', r=2): print(i, end='') ('a', 'b') ('a', 'c') ('a', 'd') ('b', 'a') ('b', 'c') ('b', 'd') ('c', 'a') ('c', 'b') ('c', 'd') ('d', 'a') ('d', 'b') ('d', 'c')4.3 itertools.combinations(iterable, r)
创建一个迭代器，返回iterable中所有长度为r的子序列，返回的子序列中的项按输入iterable中的顺序排序 (不带重复)源代码 def combinations(iterable, r): # combinations('ABCD', 2) --> AB AC AD BC BD CD # combinations(range(4), 3) --> 012 013 023 123 pool = tuple(iterable) n = len(pool) if r > n: return indices = list(range(r)) yield tuple(pool[i] for i in indices) while True: for i in reversed(range(r)): if indices[i] != i + n - r: break else: return indices[i] += 1 for j in range(i+1, r): indices[j] = indices[j-1] + 1 yield tuple(pool[i] for i in indices) 使用 from itertools import * for i in combinations('abcd',r=2): print(i, end=' ') ('a', 'b') ('a', 'c') ('a', 'd') ('b', 'c') ('b', 'd') ('c', 'd')4.4 itertools.combinations_with_replacement(iterable, r)
创建一个迭代器，返回iterable中所有长度为r的子序列，返回的子序列中的项按输入iterable中的顺序排序 (带重复)源代码 def combinations_with_replacement(iterable, r): # combinations_with_replacement('ABC', 2) --> AA AB AC BB BC CC pool = tuple(iterable) n = len(pool) if not n and r: return indices = [0] * r yield tuple(pool[i] for i in indices) while True: for i in reversed(range(r)): if indices[i] != n - 1: break else: return indices[i:] = [indices[i] + 1] * (r - i) yield tuple(pool[i] for i in indices) 使用 from itertools import * for i in combinations_with_replacement('abcd',r=2): print(i, end=' ') ('a', 'a') ('a', 'b') ('a', 'c') ('a', 'd') ('b', 'b') ('b', 'c') ('b', 'd') ('c', 'c') ('c', 'd') ('d', 'd')