英文:
Append first item to end of iterable in Python
问题
我需要将一个（通用的）可迭代对象的第一个元素追加为该可迭代对象的最后一个元素（从而“闭合循环”）。我想到了以下方法：
from collections.abc import Iterable
from itertools import chain
def close_loop(iterable: Iterable) -> Iterable:
iterator = iter(iterable)
first = next(iterator)
return chain([first], iterator, [first])
# Examples:
list(close_loop(range(5))) # [0, 1, 2, 3, 4, 0]
''.join(close_loop('abc')) # 'abca'
这个方法可以工作，但似乎有点“笨拙”。我想知道是否有更直接的方法，可以利用itertools的魔力。如果有使用more_itertools的解决方案，也非常欢迎。
英文:
I need to append the first item of a (general) iterable as the final item of that iterable (thus "closing the loop"). I've come up with the following:
from collections.abc import Iterable
from itertools import chain
def close_loop(iterable: Iterable) -> Iterable:
iterator = iter(iterable)
first = next(iterator)
return chain([first], iterator, [first])
# Examples:
list(close_loop(range(5))) # [0, 1, 2, 3, 4, 0]
''.join(close_loop('abc')) # 'abca'
Which works, but seems a bit "clumsy". I was wondering if there's a more straightforward approach using the magic of itertools. Solutions using more_itertools are also highly welcome.
答案1
得分: 6
这是一个不使用itertools的版本：
def close_loop(iterable):
iterator = iter(iterable)
first = next(iterator)
yield first
yield from iterator
yield first
英文:
Here is a version which doesn't use itertools
def close_loop(iterable):
iterator = iter(iterable)
first = next(iterator)
yield first
yield from iterator
yield first
答案2
得分: 1
使用itertools.tee：
from itertools import chain, tee
def close_loop(iterable):
orig, dupl = tee(iterable, 2)
first = next(orig)
return chain(dupl, [first])
使用itertools.tee函数：
from itertools import chain, tee
def close_loop(iterable):
orig, dupl = tee(iterable, 2)
first = next(orig)
return chain(dupl, [first])
英文:
Using itertools.tee:
from itertools import chain, tee
def close_loop(iterable):
orig, dupl = tee(iterable, 2)
first = next(orig)
return chain(dupl,[first])
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