"Martin v. Löwis", 16.05.2012 20:33: >> Does this use case make sense to everyone? >> >> The reason why we are discussing this on python-dev is that we are looking >> for a general way to expose these C level signatures within the Python >> ecosystem. And Dag's idea was to expose them as part of the type object, >> basically as an addition to the current Python level tp_call() slot. > > The use case makes sense, yet there is also a long-standing solution > already to expose APIs and function pointers: the capsule objects. > > If you want to avoid dictionary lookups on the server side, implement > tp_getattro, comparing addresses of interned strings.
I think Martin has a point there. Why not just use a custom attribute on callables that hold a PyCapsule? Whenever we see inside of a Cython implemented function that an object variable that was retrieved from the outside, either as a function argument or as the result of a function call, is being called, we try to unpack a C function pointer from it on all assignments to the variable. If that works, we can scan for a suitable signature (either right away or lazily on first access) and cache that. On each subsequent call through that variable, the cached C function will be used. That means we'd replace Python variables that are being called by multiple local variables, one that holds the object and one for each C function with a different signature that it is being called with. We set the C function variables to NULL when the Python function variable is being assigned to. When the C function variable is NULL on call, we scan for a matching signature and assign it to the variable. When no matching signature can be found, we set it to (void*)-1. Additionally, we allow explicit user casts of Python objects to C function types, which would then try to unpack the C function, raising a TypeError on mismatch. Assignments to callable variables can be expected to occur much less frequently than calls to them, so this will give us a good trade-off in most cases. I don't see why this kind of caching would be any slower inside of loops than what we were discussing so far. Stefan _______________________________________________ cython-devel mailing list cython-devel@python.org http://mail.python.org/mailman/listinfo/cython-devel
