在 python 中处理 list.index(might-not-exist) 的最佳方法? [英] Best way to handle list.index(might-not-exist) in python?
问题描述
我的代码看起来像这样:
I have code which looks something like this:
thing_index = thing_list.index(thing)
otherfunction(thing_list, thing_index)
好的,这样简化了,但你明白了.现在 thing
可能实际上不在列表中,在这种情况下,我想将 -1 作为 thing_index
传递.在其他语言中,这是您期望 index()
在找不到元素时返回的内容.事实上,它会抛出一个 ValueError
.
ok so that's simplified but you get the idea. Now thing
might not actually be in the list, in which case I want to pass -1 as thing_index
. In other languages this is what you'd expect index()
to return if it couldn't find the element. In fact it throws a ValueError
.
我可以这样做:
try:
thing_index = thing_list.index(thing)
except ValueError:
thing_index = -1
otherfunction(thing_list, thing_index)
但这感觉很脏,而且我不知道是否会因其他原因引发 ValueError
.我基于生成器函数想出了以下解决方案,但看起来有点复杂:
But this feels dirty, plus I don't know if ValueError
could be raised for some other reason. I came up with the following solution based on generator functions, but it seems a little complex:
thing_index = ( [(i for i in xrange(len(thing_list)) if thing_list[i]==thing)] or [-1] )[0]
有没有更简洁的方法来实现同样的目标?假设列表未排序.
Is there a cleaner way to achieve the same thing? Let's assume the list isn't sorted.
推荐答案
使用 try-except 子句并没有什么肮脏"之处.这是pythonic的方式.ValueError
只会由 .index
方法引发,因为它是你在那里唯一的代码!
There is nothing "dirty" about using try-except clause. This is the pythonic way. ValueError
will be raised by the .index
method only, because it's the only code you have there!
回复评论:
在 Python 中,请求宽恕比获得许可更容易 哲学已经确立,no index
不会为任何其他问题引发此类错误.不是我能想到的.
To answer the comment:
In Python, easier to ask forgiveness than to get permission philosophy is well established, and no index
will not raise this type of error for any other issues. Not that I can think of any.
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