[Python-Dev] Re: anonymous blocks

Phillip J. Eby pje at telecommunity.com
Thu Apr 28 03:12:19 CEST 2005

At 05:43 PM 4/27/05 -0700, Guido van Rossum wrote:
>Well, perhaps block *should* call iter()? I'd like to hear votes about
>this. In most cases that would make a block-statement entirely
>equivalent to a for-loop, the exception being only when there's an
>exception or when breaking out of an iterator with resource
>I initially decided it should not call iter() so as to emphasize that
>this isn't supposed to be used for looping over sequences -- EXPR1 is
>really expected to be a resource management generator (or iterator).

Which is why I vote for not calling iter(), and further, that blocks not 
use the iteration protocol, but rather use a new "block template" 
protocol.  And finally, that a decorator be used to convert a generator 
function to a "template function" (i.e., a function that returns a block 

I think it's less confusing to have two completely distinct concepts, than 
to have two things that are very similar, yet different in a blurry kind of 
way.  If you want to use a block on an iterator, you can always explicitly 
do something like this:

     def iterate(iterable):
         for value in iterable:
             yield value

     block iterate([1,2,3]) as x:
         print x

> > I wonder if generators that contain a yield-expression should
> > properly be called coroutines.  Practically, I suspect it would just
> > cause confusion.
>I have to admit that I haven't looked carefully for use cases for

Anything that wants to do co-operative multitasking, basically.

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