mutable list iterators - a proposal

[Raymond Hettinger]

[Raymond] 
> > All the contortions in the code still suggest to me that the use case
> > needs a different algorithm.  Try rewriting it with separate input and
> > output lists.  My bet is that the code is clearer and more
> > maintainable.

[Jess Austin]
> My original use case was 3 classes in 30 lines, not including the
> subclassing of list.

Depending on your application, there may be a good alternative to
mutating in-place while iterating.  Consider using a Queue object or
something similar (collections.deque in Py2.4, deque objects on ASPN,
or lists with append() and pop(0)):

while inputlist:
    datum = inputlist.pop(0)
    [processing with the element]
    if somecondition:
         inputlist.append(datum)
    else:
         continue   # effectively removing the element

The idea is to get around the issues of mutating in-place by removing
the element in question, processing it, and if needed again, adding to
the end of the queue.

The ASPN recipes on queues show show to do this a bit more efficiently
than with the list object but the idea is the same.



> I love to use it.  Iterators and list comprehensions were good, but
> coupled with itertools they are great.
> 
> Thanks, Raymond, for all you've done for Python.

Thanks for the accolades.


Raymond