从Python中的单元素列表中仅获取元素？

When a Python list is known to always contain a single item, is there way to access it other than:

当已知Python列表始终包含单个项目时，是否可以访问它而不是：

mylist[0]

You may ask, 'Why would you want to?'. Curiosity alone. There seems to be an alternative way to do everything in Python.

你可能会问，'你为什么要这样？'。仅好奇心。似乎有另一种方法可以在Python中完成所有工作。

2 个解决方案

#1

Sequence unpacking:

序列拆包：

singleitem, = mylist
# Identical in behavior (byte code produced is the same),
# but arguably more readable since a lone trailing comma could be missed:
[singleitem] = mylist

Explicit use of iterator protocol:

显式使用迭代器协议：

singleitem = next(iter(mylist))

Destructive pop:

破坏性流行音乐：

singleitem = mylist.pop()

Negative index:

负指数：

singleitem = mylist[-1]

Set via single iteration for (because the loop variable remains available with its last value when a loop terminates):

通过单次迭代设置（因为循环变量在循环终止时仍保持其最后一个值）：

for singleitem in mylist: break

Many others (combining or varying bits of the above, or otherwise relying on implicit iteration), but you get the idea.

许多其他人（结合或改变上述内容，或以其他方式依赖隐式迭代），但你明白了。

#2

I will add that the more_itertools library has a tool that returns one item from an iterable.

我将补充说，more_itertools库有一个工具可以从一个iterable中返回一个项目。

from more_itertools import one


iterable = ["foo"]
one(iterable)
# "foo"

In addition, more_itertools.one raises an error if the iterable is empty or has more than one item.

此外，如果iterable为空或具有多个项目，more_itertools.one会引发错误。

iterable = []
one(iterable)
# ValueError: not enough values to unpack (expected 1, got 0)

iterable = ["foo", "bar"]
one(iterable)
# ValueError: too many values to unpack (expected 1)

#1