Hey Simon, >> Isn't that a total mess? Is there a reason why UniqueRepresentation > >> provides __eq__ and __hash__, but not __cmp__? > >> > > > > I thought __cmp__() is only called if __eq__() is not implemented? > > I did not check the documentation before writing the following, but I > think it is as follows: > * If you do A==B then __eq__ is called, regardless of whether __cmp__ > is provided or not. > * Your class will implicitly have __eq__, __le__, __ne__ and so on, > if you implement __richcmp__ > * If you do not implement __richcmp__ but you implement __cmp__ then > again your class will implicitly have __eq__, __le__, ... > * If you provide both __richcmp__ and __cmp__, then your __richcmp__ > will be used in A==B, A<=B etc., but your __cmp__ will be used in > cmp(A,B). > > And now the catch: In a Cython class, you can not directly implement > __eq__, but you *must* implement __richcmp__ instead.
That seems strange to me... > And that's a > problem when cythoning UniqueRepresentation, because currently it is a > Python class with __eq__, __ne__ and __hash__ implemented, but not with > __richcmp__. > > And the problem with UniqueRepresentation.__richcmp__ is that one has an > obvious default for __eq__ and __ne__ (namely comparison with "is" or > "is not"), but __le__ and other comparison must be provided in another > class, because there is no obvious default. > Okay. Is there any reason why we couldn't default to comparing the string representation because I would think we would not want two different (unique) parents to have the same repr and it would give a consistent return? > > I almost feel like we should try to push comparisons by "is" (identity) > > rather than "==" (equality) for unique parents. > > Well, that is what UniqueRepresentation.__eq__ does anyway. > Point. I was thinking in the same way as None. > Also please forgive the naive question, but is there any reason for a > > Parent to not be a UniqueRepresentation? > > For a very simple reason: If your Parent is a cdef class then it simply > can not inherit from UniqueRepresentation, because it is a Python class. > > This problem will not be lifted. Even though I will try to provide a > cythoned UniqueRepresentation.__richcmp__ method, it would be impossible > to turn the Python class UniqueRepresentation into a cdef class: It > relies on a metaclass, and that's not available for extension classes. > Ah I see. That explains a few things I was curious about. Thanks! Thank you, Travis -- You received this message because you are subscribed to the Google Groups "sage-devel" group. To post to this group, send email to sage-devel@googlegroups.com. To unsubscribe from this group, send email to sage-devel+unsubscr...@googlegroups.com. Visit this group at http://groups.google.com/group/sage-devel?hl=en.
