#15348: "R.<a> =" syntactic sugar incorrect for EquationOrder
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Reporter: emassop | Owner:
Type: defect | Status: needs_review
Priority: major | Milestone: sage-7.0
Component: number fields | Resolution:
Keywords: | Merged in:
Authors: Jeroen Demeyer | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
u/jdemeyer/ticket/15348 | a354f9eef48bb882a538d53dc06e416e9fc8393c
Dependencies: | Stopgaps:
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Comment (by emassop):
Replying to [comment:30 jdemeyer]:
> Replying to [comment:28 emassop]:
> > The docstring says "This is cached, so we can manually set the result
if required".
> Fixed.
Yeah, this works :).
> > Why is it okay to change `gens_dict`, but not `gens` itself?
> Because of the way how `gens_dict()` is used: `gens_dict` is supposed to
return a dict of generators with their name as key. For example, it is
often used to name variables for an `eval()` statement. So philosophically
this is closer to `_defining_generators()` than to `gens()`.
Reading `gens_dict` as a dict version of `gens`, I would expect the same
values to be present in `gens_dict` as in `gens`. However, with `gens`
deprecated, maybe this is okay.
> > Hack: What about reordering the result of `gens()` (or probably
`basis`?) such that desired generators form a prefix?
> I would guess that would break stuff. I wouldn't be surprised if there
was code assuming that `1` is the first element of `basis()`.
Yeah, that seems likely :(. We can use such a trick to fix `R.<several
letters> =` though, by prepending `[x for x in self.number_field().gens()
if x in self]` to `remaining` in `.ring_generators`. I don't like it very
much, but I think it could work.
--
Ticket URL: <http://trac.sagemath.org/ticket/15348#comment:31>
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