JK, As a general rule, let Python call the "magic" __method__ methods behind the scenes. So don't call obj.__hash()__ or obj.__len__ or obj.__le__ just use hash(obj), len(obj) or <=. Of course there are exceptions, for example when calling the __init__() method of a supercalass inside the __init__ method of your class and perhaps a few others... Nick V.
JKPeck wrote: > Thanks for the advice. Once assured that __hash__ etc was the right > route, I found that using hash() instead of object.__hash__() gave me > stable hash valules. (I am hashing strings that I know to be unique.) > > The "no luck" situation was that a set would accept the same object > multiple times, not recognizing that it was truly the same object. > > > Nick Vatamaniuc wrote: > > JK, > > > > You are correct to implement __hash__ and __eq__. The problem is how > > you implemented them. Usually your __eq__ method should compare the > > necessary attributes of the objects for equality. The __hash__ should > > return a 32-bit integer. Your best bet is probably to return a hash of > > hashes of your attributes that are used in equality comparison. What > > this means is that your attributes used to produce the __hash__ should > > also be hashable. This is important yet not immediatly obvious. So you > > could for example return hash( (attribute1, attribute2, attribute3) ), > > where attribute1, attribute2, attribute3 are all hashable. > > Of course, you provided no code and no error messages (the > > 'SoFarNoLuck' exception is not descriptive enough ; ) > > > > Hope this helps > > > > > > > > JKPeck wrote: > > > I would like to be able use sets where the set members are objects of a > > > class I wrote. > > > I want the members to be distinguished by some of the object content, > > > but I have not figured out how a set determines whether two (potential) > > > elements are identical. I tried implementing __eq__ and __ne__ and > > > __hash__ to make objects with identical content behave as identical for > > > set membership, but so far no luck. > > > > > > I could subclass set if necessary, but I still don't know what I would > > > need to override. > > > > > > TIA for any advice you can offer. -- http://mail.python.org/mailman/listinfo/python-list
