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Date: Mon, 3 Sep 2012 13:04:23 -0700 (PDT)
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Subject: Re: set and dict iteration
From: Aaron Brady <castironpi@gmail.com>
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Xref: csiph.com comp.lang.python:28369

On Monday, September 3, 2012 2:30:24 PM UTC-5, Ian wrote:
> On Sun, Sep 2, 2012 at 11:43 AM, Aaron Brady <castironpi@gmail.com> wrote=
:
>=20
> > We could use a Python long object for the version index to prevent over=
flow.  Combined with P. Rubin's idea to count the number of open iterators,=
 most use cases still wouldn't exceed a single word comparison; we could re=
set the counter when there weren't any.
>=20
>=20
>=20
> We could use a Python long; I just don't think the extra overhead is
>=20
> justified in a data structure that is already highly optimized for
>=20
> speed.  Incrementing and testing a C int is *much* faster than doing
>=20
> the same with a Python long.

I think the technique would require two python longs and a bool in the set,=
 and a python long in the iterator.

One long counts the number of existing (open) iterators.  Another counts th=
e version.  The bool keeps track of whether an iterator has been created si=
nce the last modification, in which case the next modification requires inc=
rementing the version and resetting the flag.