查找条件为真的第一个列表元素 [英] Finding the first list element for which a condition is true

问题描述

我一直在寻找一种优雅的(简短的！)方法来返回匹配特定条件的列表的第一个元素，而不必评估列表中每个元素的条件.最终我想出了:

I was looking for an elegant (short!) way to return the first element of a list that matches a certain criteria without necessarily having to evaluate the criteria for every element of the list. Eventually I came up with:

(e for e in mylist if my_criteria(e)).next()

有更好的方法吗?

更准确地说:有内置的 Python 函数，例如 all() 和 any() - 使用类似 的函数难道没有意义吗?first() 也是吗?出于某种原因，我不喜欢在我的解决方案中调用 next().

To be more precise: There's built in python functions such as all() and any() - wouldn't it make sense to have something like first() too? For some reason I dislike the call to next() in my solution.

推荐答案

不 - 看起来不错.我很想重新写成:

Nope - looks fine. I would be tempted to re-write possibly as:

from itertools import ifilter
next(ifilter(my_criteria, e))

或者至少将计算分解为生成器，然后使用它:

Or at least break out the computation into a generator, and then use that:

blah = (my_function(e) for e in whatever)
next(blah) # possibly use a default value

另一种方法，如果你不喜欢next:

Another approach, if you don't like next:

from itertools import islice
val, = islice(blah, 1)

如果它是空的"，这会给你一个 ValueError 作为异常

That'll give you a ValueError as an exception if it's "empty"

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