itertools

itertools模块提供了非常有用的用于操作迭代器的函数.

"无限"迭代器

count()

count([step])会创建一个"无限"迭代器.

例子

>>> import itertools
>>> natuals = itertools.count(1)
>>> for n in natuals: 
...     print(n)
...
1
2
3
...

Tip

可以通过takewhile()函数根据条件判断来截取到一个有限的序列:

例子

>>> import itertools
>>> natuals = itertools.count(1)
>>> ns = itertools.takewhile(lambda x: x <= 10, natuals)
>>> list(ns)
[1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

cycle()

cycle([iterable])会把传入的可迭代对象转为一个迭代器, 并"无限"重复.

例子

>>> import itertools
>>> cs = itertools.cycle('ABC')
>>> for c in cs:
...     print(c)
...
'A'
'B'
'C'
'A'
'B'
'C'

repeat()

repeat([var], [num])会把传入的第一个元素无限重复下去, 第二个参数可以限定重复的次数, 默认为"无限".

例子

>>> import itertools
>>> ns = itertools.repeat('A', 3)
>>> for n in ns:
...     print(n)
...
A
A
A

串联可迭代对象

chain([iterable1], [iterable2])可以把一组可迭代对象串联起来, 形成一个更大的迭代器:

例子

>>> import itertools
>>> for c in itertools.chain('ABC', 'XYZ'):
...     print(c)
...
A
B
C
X
Y
Z

返回相邻重复元素

groupby([iterable])把可迭代对象中相邻的重复元素挑出来放在一起.

例子

>>> for key, group in itertools.groupby('AAABBBCCAAA'):
...     print(key, list(group))
...
A ['A', 'A', 'A']
B ['B', 'B', 'B']
C ['C', 'C']
A ['A', 'A', 'A']

Tip

可以自定义重复元素的判断标准.

例子

>>> for key, group in itertools.groupby('AaaBBbcCAAa', lambda c: c.upper()):
...     print(key, list(group))
...
A ['A', 'a', 'a']
B ['B', 'B', 'b']
C ['c', 'C']
A ['A', 'A', 'a']

只要是大写相同, 两个元素就被认为是重复元素.

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1. Itertools. (n.d.). Retrieved June 19, 2024, from https://www.liaoxuefeng.com/wiki/1016959663602400/1017783145987360 ↩