#16127: Fix comparison of PARI objects
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Reporter: pbruin | Owner:
Type: defect | Status: needs_review
Priority: critical | Milestone: sage-6.4
Component: interfaces | Resolution:
Keywords: pari comparison | Merged in:
Authors: Peter Bruin | Reviewers: Jeroen Demeyer
Report Upstream: N/A | Work issues:
Branch: | Commit:
u/pbruin/16127-pari_comparison | 0e0b4da393fa63c54e6f8c3ade0309ec198c2ffe
Dependencies: | Stopgaps:
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Comment (by pbruin):
Replying to [comment:25 jdemeyer]:
> I'm slightly worried about the fact that sorting using `cmp` is not
supported in Python 3.
I find this a strange choice, but I guess we'll have to live with it...
> It seems the Python 3 way is to define either a sorting key (which isn't
applicable here) or just use the rich comparison operators.
There are various solutions:
1. Python (3, at least) has a function `cmp_to_key` that converts a `cmp`
function into a `key` function, so instead of `cmp=cmpfunc` you can
specify `key=cmp_to_key(cmpfunc)`. (The key returned by
`cmp_to_key(cmpfunc)` for a given object `obj` is a new object wrapping
`obj` with comparison operators implemented using `cmpfunc`.) This looks
artificial and inefficient.
2. When sorting polynomials (which are the only kind of non-ordered PARI
objects that is currently sorted somewhere in the Sage library), one can
specify `key=lambda f: f.list()`.
3. Any list of PARI objects can be sorted by converting it into a `t_VEC`
and using one of several built-in PARI sorting functions.
I don't think the disappearance of the `cmp` keyword for sorting is
serious enough that it forces us to keep `__cmp__()` and `__richcmp__()`
consistent. (In principle, if we adopt 2. or 3. above, we could even
think about removing `gen._cmp_c_impl()`, so the generic `Element` code
automatically falls back to using rich comparison to implement
`__cmp__()`. I'm not sure if this is a good idea, though.)
--
Ticket URL: <http://trac.sagemath.org/ticket/16127#comment:26>
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