Opened 4 years ago

Last modified 4 years ago

#18346 closed enhancement

Easier handling of vertex labels in graph backends — at Version 2

Reported by: ncohen Owned by:
Priority: major Milestone: sage-6.7
Component: graph theory Keywords:
Cc: borassi, dcoudert, darij, vdelecroix Merged in:
Authors: Nathann Cohen Reviewers:
Report Upstream: N/A Work issues:
Branch: public/18346 (Commits) Commit: 25765bb3c4cb4c5f49e5078d7e6e3968c62310e1
Dependencies: Stopgaps:

Description (last modified by ncohen)

This ticket addresses the following problem:

In the CGraph backends, three cdef functions are used all the time to deal with vertex labels, i.e. get_vertex, vertex_label, check_vertex. They are always called with the same arguments, which are all attributes of the backend that calls it. They should be method, so that the arguments are not needlessly repeated.

What this branch does:

  • The CGraph backends (i.e. SparseBackend, DenseBackend and StaticSparseGraph) and GenericGraphBackend are turned into cdef classes.
  • The three functions get_vertex, vertex_label, check_vertex become methods of CGraphBackend
  • It adds a method CGraphBackend.c_graph() to get the two cdef attributes _cg and _cg_rev. Turns out that some code in Sage accesses directly G._backend._cg.

This should have been sufficient, but there were (unexpected) consequences:

  • There is no automatic pickling for cdef classes (as instrospection does not work), and the doctests do not pass if that does not work. Consequently, I implemented a unique __reduce__ function in GenericGraphBackend which handles the pickling for all backends (sparse/dense/static/networkx). It also removes some duplicated code as a result.

This makes the code a bit clearer (and it is needed). Also, moving this pickling function above is good for the future, for there will be many modifications in the future to the data structures in Sage: I plan to merge CGraph and GenericBackend into only one class (but that's for later).

Nathann

P.S.: The branch is built to be reviewed commit by commit. In particular, the renamed file appears as trivial when looking at the first commit, but as a lot of + and - when looking at the branch's diff

Change History (2)

comment:1 Changed 4 years ago by ncohen

  • Branch set to public/18346
  • Commit set to 25765bb3c4cb4c5f49e5078d7e6e3968c62310e1
  • Component changed from PLEASE CHANGE to graph theory
  • Status changed from new to needs_review

New commits:

9e60492trac #18346: Make graph_backends.py into a .pyx
da8479etrac #18346: Move and indent three functions (nothing else is changed)
5b765e1trac #18346: Rename calls to [get_vertex, vertex_label, check_vertex] into self.method calls
2704ddatrac #18346: Turn the backends into cdef classes
e11d4d8trac #18346: New pickling function for GraphBackend
bd8d988trac #18346: Remove old __reduce__ functions and move useful doctests
30eb626trac #18346: Some python code accesses G._backend._cg directly
25765bbtrac #18346: A 'cdef class' is a 'type', not a 'class'

comment:2 Changed 4 years ago by ncohen

  • Description modified (diff)
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