Re: Access to return / exception context in finally block

On 01/09/2025 14:26, marius.spix--- via Python-list wrote:
>> In your example when would isinstance(__exit_context__, ReturnContext)
>> be True and when would it be False? What would __exit_context__.value
>> be? I can't think of a sensible meaning for it. If no exception occurs,
>> is the value returned by f supposed to be 10/x or __exit_context__.value
>> + 1 # whatever that is
>> Best wishes
>> Rob Cliffe
> Dear Rob,
>
> isinstance(__exit_context__, ReturnContext) would only be True, when the try, except or else block is left using a return statement.
>
> __exit_context__.value  would be the return value of f(x), in that case 10/x. Currently it is not possible to access this value in the finally block, but it can be overwritten, as the return statement is compiled into a new RETURN_VALUE opcode.
>
> In this example, f(x) would return 10/x + 1 if x != 0 else 0.
>
> I think that this magic variable would make error handling much more easier. What do you think?
>
> Best wishes
>
> Marius Spix
How is this better than

def f(x):
     try:
         quot = 10 / x
     except ZeroDivisionError as exc:
         log_error(exc)
         return 0
     else:
         log_return(quot)
         return quot + 1
     finally:
         "Any cleanup processing needed before returning"


or


def f(x):
     try:
         quot = 10 / x
     except ZeroDivisionError as exc:
         log_error(exc)
         res = 0
     else:
         log_return(quot)
         res = quot + 1
     finally:
         return res


Best wishes
Rob Cliffe
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