[Python-3000] Set literal

Guido van Rossum guido at python.org
Mon Jan 28 17:02:24 CET 2008

Please don't reopen this. There are good reasons for 'set' to be the
default set type and 'frozenset' to appear like a poor cousin. For
one, their naming. This was all reasoned out long, long ago, in Python
2.3 with the sets module. If you insist I will try to write it up all
again, but I'd rather you believe that we weren't crazy back then.
Raymond's about-face suggests that there are plenty of dead alleys
that lead the traveler astray by appearing to be a shortcut to their


On Jan 27, 2008 9:38 PM, Greg Ewing <greg.ewing at canterbury.ac.nz> wrote:
> Guido van Rossum wrote:
> > On Jan 26, 2008 8:39 PM, Raymond Hettinger <python at rcn.com> wrote:
> >
> >>However, my support for it has waned anyway.  The notation is also
> >>used for set comprehension and those should be mutable.
> >
> > Cool. That saves us a PEP. Vive le status quo.
> You're changing your mind back again just like that? That's
> disappointing -- I was fairly convinced there as well.
> Another possibility would be to drop set comprehension
> syntax and just require people to use set(genexp).
> Or have set comprehensions produce frozensets and require
> set(genexp) to get a mutable set.
> On the face of it, it's not clear to me that the result of
> a set comprehension should necessarily be mutable.
> When I think about how I have used list comprehensions,
> mutability of the resulting list isn't usually a requirement.
> I don't expect this would be different with sets.
> --
> Greg
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--Guido van Rossum (home page: http://www.python.org/~guido/)

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