Hello Franck, It's really a good idea to map the Hash() OpenCascade method and the python __hash__(). I read a few posts on the __hash__() topic. A good one is, for instance: http://mail.python.org/pipermail/python-dev/2003-September/037923.html .
It's said that 'object.__hash__() returns id(obj) by default'. I tested that a little: >>> a = object() >>> a.__hash__() 10093672 >>> id(a) 10093672 >>> But, if __hash__ is overloaded, then __hash() and id() returns 2 different integers. This is then my proposition: - *for each* pythonOCC object that is managed by Handle_* (and thus, for which the HashCode() method is available), overload the __hash__ method as Frank said. It can be done within SWIG with two or three more lines in the SWIG_generator.py script. - for other pythonOCC objects, leave the default __hash__ method (thus equivalent to id() ) Thomas Frank Conradie a écrit : > Hi Jelle > > My particular need was to hash TopoDS_Shape objects properly. I'm not > sure if this is a good permanent solution, but this works for me, for > shapes at least: > > def shape_hash(self): > return self.HashCode(sys.maxint) > TopoDS.TopoDS_Shape.__hash__ = shape_hash > > Now I can use shapes in a Python set and as keys in a Python dict - > which also means that your Topology.Topo class works properly now (if > topo_item in topo_set)! > > I can't help thinking there must be a more general way to incorporate > this into the SWIG wrapper for *all* OCC classes, but I don't know > enough about swig yet to know for sure. > > Cheers, > Frank > > jelle feringa wrote: >> >> In order to use pythonocc objects in sets and as dict keys, they >> must hash to the underlying OCC object. In fact, your Topo class >> uses a set internally that does not work because of this very >> fact, because set checks for set membership via hash, and thus, >> two of the same objects that get explored will hash to different >> values and thus be passed back twice. >> >> >> Hi Frank, >> >> This is really interesting, thanks so much for explaining. >> Actually, now I recall what I messed up. I looped through a list of >> some topology, lets say vertices and checked for their id -> id(vertex). >> That did work, however as you point out hash != id. >> I think overloading the hash with comparing id()'s could work. >> >> >> Hope this makes sense. >> >> >> A lot, thanks for your advice here. >> >> >> I suppose I could overwrite __hash__ the same way you guys >> initially got past the == issue. >> >> >> What do you think of overloading hash with id? >> I'll check tomorrow morning, would be great if this is a stable fix, >> it sure could be useful. >> >> Thanks, >> >> -jelle >> > ------------------------------------------------------------------------ > > _______________________________________________ > Pythonocc-users mailing list > Pythonocc-users@gna.org > https://mail.gna.org/listinfo/pythonocc-users > _______________________________________________ Pythonocc-users mailing list Pythonocc-users@gna.org https://mail.gna.org/listinfo/pythonocc-users
