用尽的迭代器——如何处理它们? [英] exhausted iterators - what to do about them?

问题描述

(在 Python 3.1 中)(与我问的另一个问题有些相关，但这个问题是关于迭代器被耗尽.)

(In Python 3.1) (Somewhat related to another question I asked, but this question is about iterators being exhausted.)

# trying to see the ratio of the max and min element in a container c
filtered = filter(lambda x : x is not None and x != 0, c)
ratio = max(filtered) / min(filtered)

我花了半个小时才意识到问题所在(filter 返回的迭代器在到达第二个函数调用时已耗尽).我如何以最 Pythonic/规范的方式重写它?

It took me half hour to realize what the problem is (the iterator returned by filter is exhausted by the time it gets to the second function call). How do I rewrite it in the most Pythonic / canonical way?

此外，除了获得更多经验之外，我还能做些什么来避免此类错误?(坦白说，我不喜欢这个语言特性，因为这些类型的错误很容易产生，很难发现.)

Also, what can I do to avoid bugs of this sort, besides getting more experience? (Frankly, I don't like this language feature, since these types of bugs are easy to make and hard to catch.)

推荐答案

只需调用 tuple(iterator)

但是我会将该过滤器重写为列表推导式，看起来像这样

however I'd rewrite that filter as a list comprehension, which would look something like this

# original
filtered = filter(lambda x : x is not None and x != 0, c)

# list comp
filtered = [x for x in c if x is not None and x != 0]

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