#15278: Hash and equality for graphs
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Reporter: SimonKing | Owner:
Type: defect | Status: new
Priority: major | Milestone: sage-5.13
Component: graph theory | Resolution:
Keywords: | Merged in:
Authors: Simon King | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
u/SimonKing/ticket/15278 | c774057bf07b2da8539f2395555b2062428874f4
Dependencies: #12601 | Stopgaps:
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Comment (by SimonKing):
Back at questions on the static graph backend...
In `__eq__`, the following data play a role:
- `.allows_multiple_edges()`
- `.allows_loops()`
- `.order()`
- `.size()`
- `._weighted`
- vertex and edge labels, and of course start and endpoints of the edges.
For immutability, it is thus essential that these methods do not change
the answers after applying non-underscore methods.
- `._weighted` may be changed by the `.weighted(new)` method, which I thus
made respectful against mutability. So, that is settled.
- The methods mentioned above call the backend, namely:
1. `._backend.multiple_edges(None)
2. `._backend.loops(None)`
3. `._backend.num_verts()`
4. `._backend.num_edges(self._directed)`
So, my question boils down to this, Nathann: Is it possible for the static
backend that the return value of the above methods 1.--4. changes, if the
user is only using non-underscore methods on the graph? If it is not
possible, then the `__eq__` classes won't change when using the static
graph backend, and I am happy.
The hash only takes into account the tuple of vertices and edges (which
includes their labels). You have already confirmed that this is fine with
the static backend.
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Ticket URL: <http://trac.sagemath.org/ticket/15278#comment:14>
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