[Cython] weird declarations in fused types C code

Stefan Behnel stefan_ml at behnel.de
Fri May 11 13:21:28 CEST 2012

mark florisson, 11.05.2012 13:00:
> On 11 May 2012 11:54, mark florisson wrote:
>> On 11 May 2012 11:44, mark florisson wrote:
>>> On 11 May 2012 07:38, Stefan Behnel wrote:
>>>> while trying to replace the "import sys; if sys.version_info >= (3,0)" in
>>>> the fused types dispatch code by the more straight forward "if
>>>> PY_MAJOR_VERSION >= 3" (before I came to think that this particular case
>>>> only guards useless code that does the wrong thing),
>>> Yes, you made that plenty clear, sorry for thinking in terms of python
>>> code. For the record, it does do the right thing.
>>>> I noticed that the
>>>> code generates a declaration of PyErr_Clear() into the outside environment.
>>>> When used in cdef classes, this leads to an external method being declared
>>>> in the class, essentially like this:
>>>>    cdef class MyClass:
>>>>        cdef extern from *:
>>>>            void PyErr_Clear()
>>>> Surprisingly enough, this actually works. Cython assigns the real C-API
>>>> function pointer to it during type initialisation and even calls the
>>>> function directly (instead of going through the vtab) when used. A rather
>>>> curious feature that I would never had thought of.
>>> Yes, normally the parser catches that.
>>>> Anyway, this side effect is obviously a bug in the fused types dispatch,
>>>> but I don't have a good idea on how to fix it. I'm sure Mark put some
>>>> thought into this while trying hard to make it work and just didn't notice
>>>> the impact on type namespaces.
>>> I am aware of this behaviour, the thing is that the dispatcher
>>> function needs to be analyzed in the right context in order to
>>> generate an appropriate function or method in case of a cdef class
>>> (which are different from methods in normal classes even when
>>> synthesized). I thought about splitting the declarations from the
>>> actual function, and analyzing that in the module scope. Perhaps with
>>> some name mangling this can avoid names being accidentally available
>>> in user code. I don't recall if I have tried that already, but I'll
>>> give it another try.
>> Ah, I see I already split them, all that is needed is to put it in the
>> global scope now :)
> https://github.com/markflorisson88/cython/commit/3500fcd01ce6e68e76fcbabfe009eb273d7972fb

Ok, sure, works for me.


More information about the cython-devel mailing list