6.2. itertools模块中常用工具函数 ¶

6.2.1. 1.导入 itertools模块 ¶

import itertools

itertools模块中提供了近二十个迭代器工具函数，主要有三类，常用的主要有：

6.2.2. 2.无限迭代器：¶

count (start, [step])                 # 从start开始，以step为步进行计数迭代
cycle (seq)                           # 无限循环迭代seq
repeat (elem, [n])                    # 循环迭代elem

6.2.3. 3.迭代短序列：¶

chain (p, q, ...)                     #链接迭代（将p,q连接起来迭代，就像从一个序列中迭代）
compress (data, selectors)            #依据selectors中的值选择迭代data序列中的值
dropwhile (pred, seq)                 #当pred对序列元素处理结果为假时开始迭代seq后所有值
filterfalse (pred, seq)               #当pred处理为假的元素

takewhile (pred, seq)                 #与dropwhile相反
tee (it, n)                           #将it重复n次进行迭代
zip_longest (p,q,...)

6.2.4. 4.组合迭代序列 ¶

product (p, q,...[, n])               #迭代排列出所有的排列
permutations (p, r)                   #迭代序列中r个元素的排列
combinations (p, r)                   #迭代序列中r个元素的组合

4.1 代码示例 ¶

count (start, [step])

#!/usr/bin/env python
# -*- coding:utf8 -*-
# auther; 18793
# Date：2020/5/10 21:32
# filename: sample1.py
import itertools

for i in itertools.count(1, 3):
    print(i)
    if i >= 10:
        break

"""
1
4
7
10
"""

cycle (seq)

import itertools

x = 0
for i in itertools.cycle(['a', 'b']):
    print(i)
    x += 1
    if x > 6:
        break

"""
a
b
a
b
a
b
a
"""

repeat (elem, [n])

import itertools

print(list(itertools.repeat(3, 3)))

#[3, 3, 3]

chain (p, q, ...)

print(list(itertools.chain([1, 3], [2, 3])))

#[1, 3, 2, 3]

compress (data, selectors)

print(list(itertools.compress([1, 2, 3, 4], [1, [], True, 3])))

dropwhile (pred, seq)

print(list(itertools.dropwhile(lambda x: x > 6, [8, 9, 1, 2, 8, 9])))
# [1, 2, 8, 9]

filterfalse (pred, seq)

print(list(itertools.takewhile(lambda x: x > 10, [18, 19, 1, 21, 8, 9])))
# [18, 19]

tee (it, n)

import itertools

for its in itertools.tee([0, 1], 2):
    for it in its:
        print(it)

'''
0
1
0
1
'''

permutations (p, r)

import itertools

print(list(itertools.permutations('abc', 2)))
# [('a', 'b'), ('a', 'c'), ('b', 'a'), ('b', 'c'), ('c', 'a'), ('c', 'b')]

combinations (p, r)

print(list(itertools.combinations('abc', 2)))
# [('a', 'b'), ('a', 'c'), ('b', 'c')]

使用无限迭代器时，必须有迭代退出的条件，否则会导致死循环。

4.2 itertools模块 ¶

#!/usr/bin/env python
# -*- coding:utf8 -*-
# auther; 18793
# Date：2019/6/17 14:00
# filename: itertools模块.py
import itertools

print([e for e in dir(itertools) if not e.startswith("_")])

import itertools as it

# 使用count(10,3)生成13、16、19....的迭代器
for e in it.count(10, 3):
    print(e)
    if e > 20:
        break
    print("---------------------")

my_counter = 0
# cycle用于对序列生成无限循环的迭代器
for e in it.cycle(["python", "kotlin", "Swift"]):
    print(e)
    # 用于跳出无限循环
    my_counter += 1
    if my_counter > 7:
        break
print("--------------------------")

# repeat用于生成n个元素重复的迭代器
for e in it.repeat("python", 3):
    print(e)

输出信息

['accumulate', 'chain', 'combinations', 'combinations_with_replacement', 'compress', 'count', 'cycle', 'dropwhile', 'filterfalse', 'groupby', 'islice', 'permutations', 'product', 'repeat', 'starmap', 'takewhile', 'tee', 'zip_longest']
10
---------------------
13
---------------------
16
---------------------
19
---------------------
22
python
kotlin
Swift
python
kotlin
Swift
python
kotlin
--------------------------
python
python
python

6.2. itertools模块中常用工具函数¶

6.2.1. 1.导入 itertools模块¶