#13394: Write a WeakValueDictionary with safer key removal
-------------------------------------+-------------------------------------
Reporter: nbruin | Owner: rlm
Type: enhancement | Status: needs_review
Priority: major | Milestone: sage-5.13
Component: memleak | Resolution:
Keywords: | Merged in:
Authors: Simon King | Reviewers:
Report Upstream: None of the above | Work issues:
- read trac for reasoning. | Commit:
Branch: | 70a7b8accb2d2156f315cbae2511985936977670
u/SimonKing/ticket/13394 | Stopgaps:
Dependencies: |
-------------------------------------+-------------------------------------
Comment (by nbruin):
I couldn't resist trying to implement our extra primitive straight onto
python's dict. It turns out to be fairly straightforward after reading
`lookdict_string` and `PyDict_DelItem` in Python's `Objects/dictobjec.c`.
As an example:
{{{
sage: %attach deldict_exact.pyx
Compiling ./deldict_exact.pyx...
sage: D={}
sage: L=[]
sage: for n in prime_range(2,100):
....: R=Integers(n)
....: k=R(1)
....: L.append(k)
....: D[R(1)]=n
....:
sage: len(D)
25
sage: init_dummy()
sage: for l in L[3:10]:
....: del_dictitem_exact(D,l,hash(l))
....:
sage: len(D)
18
sage: set(L[:3]+ L[10:]) == set(D.keys())
True
}}}
So the interface is: `del_dictitem_exact(D,key,hash)`, where `hash` is
`hash(key)` (but is separately supplied for efficiency). This routine
removes the entry `D[key]` if `key` identically occurs as a key in `D`. We
could match on value too if we want, but these semantics make most sense
for a dictionary.
Problematic/hackish things:
- I have hardcoded PERTURB_SHIFT since that constant isn't available
outside `dictobject.c`.
- I had to write a programmatic routine to go looking for the `dummy`
sentinel key value (which is used to mark deleted entries)
- I am relying on the internals of `PyDictEntry` and `PyDictObject`.
However, I'm getting those from `Python.h`, so we shouldn't get silent
failure on those.
With this extra primitive you could write a safer callback on
`WeakValueDictionary` without needing the extra indirection. You'd call
`init_dummy` upon instantiation of a !WeakValueDictionary, to ensure that
it's initialized.
--
Ticket URL: <http://trac.sagemath.org/ticket/13394#comment:25>
Sage <http://www.sagemath.org>
Sage: Creating a Viable Open Source Alternative to Magma, Maple, Mathematica,
and MATLAB
--
You received this message because you are subscribed to the Google Groups
"sage-trac" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to [email protected].
To post to this group, send email to [email protected].
Visit this group at http://groups.google.com/group/sage-trac.
For more options, visit https://groups.google.com/groups/opt_out.
