[Python-ideas] Possible new itertool: comm()

Antoine Pitrou solipsis at pitrou.net
Tue Jan 6 19:36:55 CET 2015

On Tue, 6 Jan 2015 18:22:44 +0000
Paul Moore <p.f.moore at gmail.com> wrote:
> On 6 January 2015 at 17:14, Raymond Hettinger
> <raymond.hettinger at gmail.com> wrote:
> >> On Jan 6, 2015, at 8:22 AM, Paul Moore <p.f.moore at gmail.com> wrote:
> >>
> >> In writing a utility script today, I found myself needing to do
> >> something similar to what the Unix "comm" utility does - take two
> >> sorted iterators, and partition the values into "only in the first",
> >> "only in the second", and "in both" groups.
> >
> > As far as I can tell, this would be a very rare need.
> It's come up for me a few times, usually when trying to check two
> lists of files to see which ones have been missed by a program, and
> which ones the program thinks are present but no longer exist.

Why don't you use sets for such things? Your iterator is really only
useful for huge or unhashable inputs.



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