一、前言
本文介紹python標準庫itertools，為了方便，直接貼**實現。
二、**實現
1、排列
tmp = itertools.permutations([1, 2, 3], 2)
print(list(tmp))#[(1, 2), (1, 3), (2, 1), (2, 3), (3, 1), (3, 2)]
tmp = itertools.combinations([1, 2, 3], 2)
print(list(tmp))#[(1, 2), (1, 3), (2, 3)]
tmp = itertools.chain.from_iterable([[1, 2], [3, 4]])
print(list(tmp))#[1, 2, 3, 4]
tmp = itertools.product([1, 2, 3], [4, 5])
print(list(tmp))#[(1, 4), (1, 5), (2, 4), (2, 5), (3, 4), (3, 5)]
import itertools
def n_gram(arr, n):
stop = none
tmp = (itertools.islice(arr, start, stop) for start in range(n))#第三個引數step預設為1
return zip(*tmp)
print(list(n_gram([1, 2, 3, 4, 5, 6], 2)))#[(1, 2), (2, 3), (3, 4), (4, 5), (5, 6)]
#上述過程的解釋
tmp1 = list(itertools.islice([1, 2, 3, 4, 5, 6], 0, none))#[1, 2, 3, 4, 5, 6]
tmp2 = list(itertools.islice([1, 2, 3, 4, 5, 6], 1, none))#[2, 3, 4, 5, 6]
t*** = (tmp1, tmp2)#([1, 2, 3, 4, 5, 6], [2, 3, 4, 5, 6])
tmp4 = zip(*t***)
print(list(tmp4))#[(1, 2), (2, 3), (3, 4), (4, 5), (5, 6)]
x = [1, 2, 3, 4, 5]
y = ['a', 'b', 'c']
res1 = zip(x, y)
print(list(res1))#[(1, 'a'), (2, 'b'), (3, 'c')]
res2 = itertools.zip_longest(x, y)
print(list(res2))#[(1, 'a'), (2, 'b'), (3, 'c'), (4, none), (5, none)]
tmp1 = itertools.accumulate([5, 15, 16, 2, 7])
print(list(tmp1))#[5, 20, 36, 38, 45]
tmp2 = itertools.accumulate([5, 15, 16, 2, 7], min)
print(list(tmp2))#[5, 5, 5, 2, 2]
t*** = itertools.accumulate([5, 15, 16, 2, 7], max)
print(list(t***))#[5, 15, 16, 16, 16]
tmp = itertools.filte***lse(bool, [none, false, 0, , 1])
print(list(tmp))#[none, false, 0, ]
import itertools
import operator
tmp = itertools.starmap(operator.mul, [(1, 2), (3, 4)])
print(list(tmp))#[2, 12]
tmp1 = itertools.takewhile(lambda x : x < 4, [1, 2, 3, 4, 5, 6])
print(list(tmp1))#[1, 2, 3]
tmp2 = itertools.dropwhile(lambda x : x < 4, [1, 2, 3, 4, 5, 6])
print(list(tmp2))#[4, 5, 6]
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