[Python-ideas] except expression

[MRAB]

On 2014-02-18 15:40, Chris Angelico wrote:
> On Wed, Feb 19, 2014 at 2:30 AM, Rob Cliffe <rob.cliffe at btinternet.com> wrote:
>> Sorry, but this seems to me to be a futile discussion.
>> Expressions can contain functions.
>> Functions can raise any exception they like.
>> So evaluating an expression can raise any exception you care to name.
>
> Of course it could raise anything, but what are you likely to want to
> catch and handle by returning a different value?
>
> LookupError when your cache isn't populated
> UnicodeDecodeError to fall back on a different encoding ("try UTF-8;
> if that fails, assume the other end is Windows and try CP-1252" - I
> have that logic in some places)
> ZeroDivisionError and return float("inf"), float("nan"), or 0
>
> But you wouldn't want to catch:
>
> SyntaxError
> ImportError
> AssertionError
> IndentationError
> ProgrammerIsAMoronAndHisCodeIsInError
>
I think that last one should be:

     ProgrammerIsAMoronAndHisCodeIsInErrorError

or just:

     PebkacError

> because most of them wouldn't come up in an expression context, and if
> they do, you aren't likely to have a useful alternate value to return.
>
> So it is conceivable that there be some tuple or superclass of "common
> errors worth catching". Trouble is, it still often wouldn't be
> appropriate to catch them all - maybe you want to hook into
> LookupError, but accidentally catching a UnicodeDecodeError along the
> way would mask a bug.
>