#10448: Extensions of ZZ are not unique parents
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Reporter: SimonKing | Owner: davidloeffler
Type: defect | Status: needs_work
Priority: major | Milestone: sage-4.7
Component: number fields | Keywords: uniqueness of parents
Author: Simon King | Upstream: N/A
Reviewer: | Merged:
Work_issues: Breaks garbage collection |
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Comment(by SimonKing):
Hi David,
Currently I try to produce a patch according to your suggestions. However:
Replying to [comment:11 davidloeffler]:
> There is a risk of this breaking garbage collection of number fields.
>
> The number field code is quite carefully written so that number fields
are globally unique...
That's not true.
{{{
sage: K.<z7> = QuadraticField(7)
sage: K is loads(dumps(K))
False
}}}
> The best solution I can think of would be to store orders in a cache
which was itself an attribute of the parent number field. This could be
implemented by making {{{order}}} tuplify its arguments and then call a
second *method* {{{_order_from_cache}}}, implemented using
{{{@cached_method}}} as usual.
Doing so, there is indeed uniqueness of orders, and that should also be
useful for pickling. However, number fields are not unique parents, and so
orders can only be unique in their number fields, but not globally.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/10448#comment:12>
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