Comment on PEP-0322: Reverse Iteration Methods

[John Roth]

I think it says what needs to be said.

+1

John Roth

"Raymond Hettinger" <vze4rx4y at verizon.net> wrote in message
news:95rcb.2002$yU5.1775 at nwrdny01.gnilink.net...
> Please comment on the new PEP for reverse iteration methods.
> Basically, the idea looks like this:
>
>      for  i in xrange(10).iter_backwards():    # 9,8,7,6,5,4,3,2,1,0
>            <do something with i>
>
> The HTML version is much more readable than the ReST version.
> See:
>          http://www.python.org/peps/pep-0322.html
>
>
> Several interesting ideas surfaced in the pre-pep thread:
>
> * Call it ireverse() instead of iter_backwards().
>
>    Good idea.  This is much more pithy.
>
>
> * Use object properties instead of methods.
>
>    I can't yet claim to understand what the author is really
>    proposing.  It has something to do which providing
>    access to an object that responds to iter, getitem, and
>    getslice with reversed indices.
>
>
> * using a single function that looks for an __riter__ magic
>    method and, if not found, use __getitem__ and __len__
>    to build a reverse iterator.
>
>    A workable version of this was posted.
>    It saves implementing some object methods at the
>       expense of adding a new builtin function and of
>       creating a new magic method name.
>    It is slower than direct access to the underlying object.
>    It crashes when applied to an infinite iterator.
>    It produces bizarre results when applied to mappings.
>
>
> * special markers for infinite iterators
>
>    This idea is interesting but doesn't extend well
>    when the object is wrapped by another iterator.
>    Also, there is no automatic way to determine
>    which generators can be infinite.
>
>
> Raymond Hettinger
>
>