Hi!
While I am at it: Why isn't there a __hash__ method for
sage.structure.SageObject written in Cython that can be inherited from
all elements and parents and needs not to be overridden? In
particular, needs not to be overridden by a slow Python method?
I mean something like
sage: cython("""
cdef class bla:
cdef object __hash
def __hash__(self):
if self.__hash is not None:
return self.__hash
self.__hash = self._hash_()
return self.__hash
""")
sage: class Foo(bla, object):
....: def _hash_(self):
....: return hash(repr(self))
....:
sage: f = Foo()
sage: %timeit hash(f)
625 loops, best of 3: 213 ns per loop
Compare this with the current default __hash__:
sage: P = Parent()
sage: %timeit hash(P)
625 loops, best of 3: 18.9 µs per loop
Hence, for implementing the hash, the user provides _hash_ rather than
__hash__.
Storing the hash value should be possible, since mutable objects are
not supposed to be hashable, right?
Of course, that would mean a lot of dull work, namely: Rename any
__hash__ method into _hash_, for any class derived from SageObject.
And also "of course", one may provide the possibility to make a class
unhashable.
But I think if all SageObjects would only need 213 ns rather than 18.9
µs to return their hash, one could get a very decent general speed-up
of Sage. So, the dull work could be worth it, isn't it?
Best regards,
Simon
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