[Python-Dev] Breaking off Enhanced Iterators PEP from PEP 340

[Guido van Rossum]

> Enhanced Iterators:
> 
> ...
> > When the *initial* call to __next__() receives an argument
> > that is not None, TypeError is raised; this is likely caused
> > by some logic error.

[Jim Jewett]
> This made sense when the (Block) Iterators were Resources,
> and the first __next__() was just to trigger the setup.
> 
> It makes less sense for general iterators.
> 
> It is true that the first call in a generic for-loop couldn't
> pass a value (as it isn't continued), but I don't see anything
> wrong with explicit calls to __next__.
> 
> Example:  An agent which responds to the environment;
> the agent can execute multi-stage plans, or change its mind
> part way through.
> 
>    action = scheduler.__next__(current_sensory_input)

Good point. I'd be happy if the requirement that the first __next__()
call doesn't have an argument (or that it's None) only applies to
generators, and not to iterators in general.

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