PEP 234: Iterators

[Just van Rossum]

"Rainer Deyke" <root at rainerdeyke.com> writes:

[ getting an exception when you modify a dict during iteration ]
> It would be nice if this could be made reliable.

Michael Hudson wrote:

> Tricky, that.  It could be made somewhat more reliable, but I think
> making it totally certain would have prohibitive drawbacks,
> particularly as stuff like:
> 
> for i in d:
>     d[i] += 1
> 
> *is* supported.

I think you get a RuntimeError if the dictionary gets resized: the dict
iterator object can check cheaply for that event. Perhaps if the dict
object grew a magic counter, which would get incremented when a new
key is added or a key is deleted, and the dict iterator would check for
*that* value, this would be more reliable. I can't judge whether this
approach would be too expensive or not.

Just