[Python-ideas] syntax to continue into the next subsequent except block

[Steven D'Aprano]

On 17/09/12 10:11, Greg Ewing wrote:
> Guido van Rossum wrote:
>> The suggestion to add ad-hoc "if <condition>" clauses to random parts
>> of the syntax doesn't appeal to me at all.
>
> I wouldn't call it a random part of the syntax. This is
> not like the proposals to add if-clauses to while loops,
> for loops, etc -- they would just be minor syntactic sugar.
> This proposal addresses something that is quite awkward to
> express using existing constructs.

I don't think it is quite awkward. Instead of the proposed:


try:
     something()
except ValueError as ex if condition(ex):
     spam()
except ValueError:
     # if not condition, fall through to the next except block
     ham()

this can be easily written as:

try:
     something()
except ValueError as ex:
     if condition(ex):
         spam()
     else:
         ham()

which costs you an indent level, which is not a big deal. (If your
code is so deeply nested that it is a big deal, it is already in
desperate need of refactoring.)


Instead of the original proposal to add a "continue" statement to
skip to the next except block:

try:
     something()
except HTTPError as ex:
     if condition(ex): continue  # skip to the next except clause
     spam()
except URLError as ex:
     ham()


we can do:


try:
     something()
except (HTTPError, URLError) as ex:
     # Technically, we don't even need to list HTTPError, since it
     # is a subclass it will be caught by URLError too.
     if type(ex) is URLError or condition(ex):
         ham()
     else:
         spam()


Have I missed any suggested use-cases?

I don't think any of the existing solutions are that awkward or
unpleasant to require new syntax. They're actually quite
straightforward.



-- 
Steven