[Python-Dev] RE: PEP-317

[Michael Chermside]

Guido writes:
> It would be simple enough to introduce new-style exceptions if
> Exception were made a new-style class and at the same time all
> new-style exceptions were required to derive from Exception:
> 
>   raise x
> 
> would check whether x was:
> 
>   - a string (but not an instance of a true subclass of str)
>   - a classic class
>   - an instance of a classic class
>   - Exception or a subclass thereof
>   - an instance of Exception or of a subclass thereof
> 
> Where the first three cases are for backward compatibility.
> 
> Similarly, the rule for
> 
>   raise x, y
> 
> should allows x to be
> 
>   - a string
>   - a classic class
>   - Exception or a subclass thereof
> 
> and in the last two cases, y could either be an instance of x (or of a
> subclass of x!), or an argument for x, or a tuple of arguments for x.

Okay, after hearing this (plus all the arguments about PEP 317
requiring an excessive level of migration pain), I am now convinced.

If the PEP winds up being officially rejected, I propose that it
grow a "rejection reasons" section explaing why, and that this section
also describe the above plan as the "plausible alternative" to PEP 317
for eventual migration to new-style exceptions.

-- Michael Chermside