I've just been struggling with understanding how inheritance and
__richcmp__ are related. Here is my example code:
cdef class A:
cdef int a
def __init__(self, a):
self.a=a
def __hash__(self):
return self.a
def __richcmp__(A self, A other, int op):
print "using op: ",op
if op == 2: # ==
return self.a == other.a
cdef class B(A):
def __init__(self, a):
self.a=a+1
def __hash__(self):
return self.a*2
Mike Hansen found some reference somewhere that said that either all of
__hash__, __richcmp__, and __cmp__ are inherited or none are (I didn't
see this in the manual, but maybe I was looking in the wrong place??).
So, predictably:
sage: A(2)==A(2)
using op: 2
True
sage: B(2)==B(2)
False
However, the confusing part is this:
sage: B(2).__eq__(B(2))
using op: 2
True
Also, unlike most other special methods, I noticed that if I defined
__richcmp__ as below (removing the type declaration for self):
def __richcmp__(self, A other, int op):
print "using op: ",op
if op == 2: # ==
return self.a == other.a
then self can't access the cdef'd "a" attribute. I think most other
commands recognize that self is of type A. That took a bit to figure
out, and I don't remember that being in the Cython docs either.
Thanks,
Jason
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