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
Sorry, but it looks really confusing to have a statement
return 10 / x which does not (let us say) raise an exception, yet does 
not represent the actual value returned by the function. Sure, you can 
already do this: def f(x): try: return 1 # Does not return except 
Exception: pass finally: return 2 # Actually returns 2 but it is IMO 
emphatically not something that should be encouraged. Best wishes Rob 
Cliffe