[Python-Dev] Re: PEP 218 (sets); moving set.py to Lib

[Guido van Rossum]

[Guido]
> > - The set constructors have an optional second argument, sort_repr,
> >   defaulting to False, which decides whether the elements are sorted
> >   when str() or repr() is taken.  I'm not sure if there would be
> >   negative consequences of removing this argument and always sorting
> >   the string representation.

[François]
> Unless there is something deep attached to the properties of the sets
> themselves, I do not understand why the sorting/non-sorting virtues of
> `repr' should be tied with the constructor.
> 
> There is a precedent with dicts.  They print non-sorted, but they
> pretty-print (through the `pprint' module) sorted.  Maybe the same could
> be done for sets: use `pprint' if you want a sorted representation.
> But otherwise, sets as well as dicts should print using the same order
> by which elements are to be iterated upon or listed, in various other
> circumstances.

This is a pretty convincing argument.  If dicts can survive being
rendered unsorted, then so can Sets.  Maybe I should remove the
sort_repr argument altogether; it's easy enough for the test suite to
use some other trick.  But for now, I'll just leave sort_repr=False
in.  I'm gonna check this in now, but that doesn't mean we can't tweak
the API or implementation, so keep those comments coming!

--Guido van Rossum (home page: http://www.python.org/~guido/)