On Sun, May 13, 2012 at 12:11 PM, Bob Grommes <bob.grom...@gmail.com> wrote: > Noob alert: writing my first Python class library. > > I have a straightforward class called Utility that lives in Utility.py. > > I'm trying to get a handle on best practices for fleshing out a library. As > such, I've done the following for starters: > > def __str__(self): > return str(type(self)) > > # def __eq__(self,other): > # return hash(self) == hash(other) > > The commented-out method is what I'm questioning. As-is, I can do the > following from my test harness: > > u = Utility() > print(str(u)) > print(hash(u)) > u2 = Utility() > print(hash(u2)) > print(hash(u) == hash(u2)) > > However if I uncomment the above _eq_() implementation, I get the following > output: > > <class 'Utility.Utility'> > Traceback (most recent call last): > File "/Users/bob/PycharmProjects/BGC/Tests.py", line 7, in <module> > print(hash(u)) > TypeError: unhashable type: 'Utility' > > Process finished with exit code 1 > > Obviously there is some sort of default implementation of __hash__() at work > and my implementation of _eq_() has somehow broken it. Can anyone explain > what's going on?
See the 3rd, 5th, and 4th paragraphs of: http://docs.python.org/dev/reference/datamodel.html#object.__hash__ Also, for future reference, it's advisable to state whether your question concerns Python 2.x or Python 3.x. Cheers, Chris -- http://chrisrebert.com -- http://mail.python.org/mailman/listinfo/python-list
