How to handle exceptions in a list comprehensions?

Question

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

For instance, if I have:

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

[1/egg for egg in eggs]

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

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

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

But this looks a bit cumbersome to me.

Is there a better way to do this in Python?

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.

Answer 1

I realize this question is quite old, but you can also create a general function to make this kind of thing easier:

def catch(func, handle=lambda e : e, *args, **kwargs):
    try:
        return func(*args, **kwargs)
    except Exception as e:
        return handle(e)

Then, in your comprehension:

eggs = (1,3,0,3,2)
[catch(lambda : 1/egg) for egg in eggs]
[1, 0, ('integer division or modulo by zero'), 0, 0]

You can of course make the default handle function whatever you want (say you'd rather return 'None' by default).

Hope this helps you or any future viewers of this question!

Note: in python 3, I would make the 'handle' argument keyword only, and put it at the end of the argument list. This would make actually passing arguments and such through catch much more natural.