[Python-Dev] Re: anonymous blocks

Greg Ewing greg.ewing at canterbury.ac.nz
Thu Apr 28 08:26:39 CEST 2005

Neil Schemenauer wrote:

> The translation of a block-statement could become:
>         itr = EXPR1
>         arg = None
>         while True:
>             try:
>                 VAR1 = next(itr, arg)
>             except StopIteration:
>                 break
>             try:
>                 arg = None
>                 BLOCK1
>             except Exception, exc:
>                 err = getattr(itr, '__error__', None)
>                 if err is None:
>                     raise exc
>                 err(exc)

That can't be right. When __error__ is called, if the iterator
catches the exception and goes on to do another yield, the
yielded value needs to be assigned to VAR1 and the block
executed again. It looks like your version will ignore the
value from the second yield and only execute the block again
on the third yield.

So something like Guido's safe_loop() would miss every other

I think Guido was right in the first place, and __error__
really is just a minor variation on __next__ that shouldn't
have a separate entry point.


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