> My knowledge of Python's iterators is kind of sketchy, so I may have missed
> something.
The only thing a python iterator really is is something that supports a
next()-method and will raise a StopIteration-Exception in case of
exhaustion.
So - nobody stops you from introducing an object like
class Foo:
def next(self):
pass
def prev(self):
pass
and work with it as you like - the same way as in C++. But the syntactic
sugaring and support in lots of classes that makes the iterator concept
especially interesting in python makes only sense in one-way-iterators.
Or do you really have a use-case for an reverting-in-the-middle for . in
. - syntax?
And as Heiko explained (and you yourself mentioned too):
forward/backward iteration makes only sense in case of a memory-backed
implementation, namely containers. But the much more general concept of
iterators of python applies to generators/generator expressions,
itertools and so on.
Diez
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