如何处理列表推导式中的异常? [英] How to handle exceptions in a list comprehensions?

问题描述

我在 Python 中有一些列表推导式，其中每次迭代都可以抛出异常.

I have some a list comprehension in Python in which each iteration can throw an exception.

例如，如果我有:

eggs = (1,3,0,3,2)

[1/egg for egg in eggs]

我会在第三个元素中遇到 ZeroDivisionError 异常.

I'll get a ZeroDivisionError exception in the 3rd element.

如何处理此异常并继续执行列表推导式?

How can I handle this exception and continue execution of the list comprehension?

我能想到的唯一方法是使用辅助函数:

The only way I can think of is to use a helper function:

def spam(egg):
    try:
        return 1/egg
    except ZeroDivisionError:
        # handle division by zero error
        # leave empty for now
        pass

但这对我来说看起来有点麻烦.

But this looks a bit cumbersome to me.

在 Python 中是否有更好的方法来做到这一点?

Is there a better way to do this in Python?

注意:这是我设计的一个简单示例(参见上面的例如")，因为我的真实示例需要一些上下文.我对避免除以零错误不感兴趣，但对处理列表理解中的异常不感兴趣.

Note: This is a simple example (see "for instance" above) that I contrived because my real example requires some context. I'm not interested in avoiding divide by zero errors but in handling exceptions in a list comprehension.

推荐答案

Python 中没有内置表达式可以让您忽略异常(或在出现异常时返回替代值 &c)，所以这是不可能的，从字面上讲，处理列表推导中的异常"，因为列表推导是一个包含其他表达式的表达式，仅此而已(即，no 语句，并且只有语句可以捕获/忽略/处理异常).

There is no built-in expression in Python that lets you ignore an exception (or return alternate values &c in case of exceptions), so it's impossible, literally speaking, to "handle exceptions in a list comprehension" because a list comprehension is an expression containing other expression, nothing more (i.e., no statements, and only statements can catch/ignore/handle exceptions).

函数调用是表达式，函数体可以包含您想要的所有语句，因此，正如您所注意到的，将易发生异常的子表达式的计算委托给函数是一种可行的解决方法(其他人，当可行的是，检查可能引发异常的值，正如其他答案中所建议的那样).

Function calls are expression, and the function bodies can include all the statements you want, so delegating the evaluation of the exception-prone sub-expression to a function, as you've noticed, is one feasible workaround (others, when feasible, are checks on values that might provoke exceptions, as also suggested in other answers).

对如何处理列表推导式中的异常"这个问题的正确回答都表达了所有这些真理的​​一部分:1) 从字面上看，即在推导式本身的词汇上，你不能；2) 实际上，您可以将工作委托给一个函数，或者在可行的情况下检查容易出错的值.因此，您一再声称这不是答案是毫无根据的.

The correct responses to the question "how to handle exceptions in a list comprehension" are all expressing part of all of this truth: 1) literally, i.e. lexically IN the comprehension itself, you can't; 2) practically, you delegate the job to a function or check for error prone values when that's feasible. Your repeated claim that this is not an answer is thus unfounded.

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