[Python-Dev] Merging PEP 310 and PEP 340-redux?

[Guido van Rossum]

[Steven Bethard]
> +0.  I'm not thoroughly convinced that generators are that much easier
> to read than a class.  But I don't find them hard to read, and I think
> it would only take a little effort to learn that generators might not
> always be intended to build iterators.

I am proposing (like Phillip Eby in his response to PEP 340) to use a
special decorator that turns a generator into a "do-template", so the
intention is evident from the generator declaration.

> If we do support generators in do-statements, I'd like their
> __enter__() and __exit__() methods (if possible) to have semantics
> like Nick Coghlan suggested[1], so that:
>  * __enter__() raises an exception if next() has already been called, and
>  * __exit__() raises an exception if StopIteration is not raised

I guess you missed my post where I gave the code for the decorator; it
does exactly that.

> The simpler semantics give you the difference between a normal exit
> and an exceptional exit.  I'd like to see an example that needs to
> know the difference between block completion exit and a
> break/continue/return exit before I'd want to make PEP 340 redux this
> much more complex.

I agreed to that in my response to Phillip Eby. I do want to pass the
exception into __exit__ so that it can be logged, for example.

-- 
--Guido van Rossum (home page: http://www.python.org/~guido/)