I don't think the key makes any guarantees, other than that the prefer will be
platform and python version independent. It also should be very hard to produce
two different objects with the same key.
It was probably originally designed to give the same ordering to reduce the
pain of transition, but I don't see any reason why it should stay that way
forever.
Aaron Meurer
Sent from my iPhone.
> On Oct 2, 2013, at 2:53 PM, Matthew Brett <matthew.br...@gmail.com> wrote:
>
> Hi,
>
> I just noticed this:
>
> In [38]: a = sympy.Symbol('a')
>
> In [39]: b = sympy.Dummy('b')
>
> In [40]: sorted([a, b])
> Out[40]: [a, _b]
>
> In [41]: sorted([a, b], key=sympy.default_sort_key)
> Out[41]: [_b, a]
>
> for sympy versions 0.7.0 through 0.7.3. Sorting without a key raises
> an error for current trunk.
>
> Is the difference between 'sort' and 'sort(key=default_sort_key)' intended?
>
> I guess, now sympy raises an error without a key, there isn't much to
> do, but maybe the change is worth recording, even if only in this
> email.
>
> Thanks,
>
> Matthew
>
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