itertools

counter()

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

cycle()

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

repeat()

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

takewhile()

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

chain()

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

groupby()

>>> 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']

>>> 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']

小結itertoolsモジュールは、すべて反復機能を処理する関数を提供し、それらの戻り値はlistではなくIteratorであり、forサイクル反復を使用する場合にのみ計算されます.