On Apr 9, 4:11 pm, Robert Bradshaw <rober...@math.washington.edu>
wrote:
> To let x.foo() call different functions depending on whether your in
> Cython or Python, or even worse whether x is fully typed, would be
> even more surprising.
Does cython overload on type signature? I don't have a particular
problem with the semantics of cpdef, it's quite reasonable to have
something like that (python semantics, but an optimized common path).
I was just expecting it to be fully equivalent with
cdef _private_cdef_method(...):
...
def method(...):
return _private_cdef_method(...)
with some magic to directly use _private_cdef_method wherever that
definition is available.
Incidentally, cpdef methods already have a way to bypass the attribute
lookup dispatch: they grow an extra parameter skip_dispatch. The
python wrapper actually calls it that way, because by the time that
gets called, all attribute lookup has already been done appropriately.
So if we could actually call
cpdeffed_method(...,skip_dispatch=1)
(which would then have to be translated to the appropriate C-code), we
would already have (something very close to) the fast path. I'm sure
there are better notations for this.
Another (slightly less flexible) possibility would be a decorator
@cython.no_dispatch
cpdef ....
which would leave out the dispatch part of a cpdef method.
Of course, we should probably first come up with a practical example
where this makes a measurable difference. However, given the trivial
access routines that some sage code has, I'd expect we could find such
an example. Making access to that attribute the critical part of a
loop might be a bit of a stretch though.
> I bet we could leverage tp_version_tag though, I'm going to give that a try.
Nope. That just tracks modifications of tp_dict, the MRO, and
modifications to tp_dict higher up in the MRO. I'm assuming that the
lookup in the vtab is already taking care of modifications there. It
seems to me that if a subtype decides to shadow a cpdef using an entry
in its tp_dict, while not touching the vtab and keeping
tp_dictoffset=0, the current dispatch code would not pick it up
anyway. Or would that be illegal according to python protocols?
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