On Thu, May 30, 2013 at 3:08 PM, Nikita Nemkin <nik...@nemkin.ru> wrote: > > > In pkg-db.pxi, this line: > > return Pkg(<object>pkg) > > and in pkg-pkg.pxi this line: > > def __cinit__(self, pkg): > self._pkg = <c_pkg.pkg *>pkg > > are the problem. > > Thanks, Nikita! That was the problem indeed :)
The funny part is that I was looking for a way to actually pass a C pointer to __cinit__ and doing it that way the compiler didn't complain at all. In fact it used to work, until I've removed Python debug symbols and then I started seeing surprises :) > You are trying to pass a C pointer to __cinit__. What actually > happens is that, because of the <object> cast, Cython treats pkg as > as Python object _itself_ and tries to do some object operations on it. > > Two ways to solve this (really common) problem: > > 1) Pass your pointer as a real python object containing the integer value > of the pointer: > > def __cinit__(self, pkg): > self._pkg = <c_pkg.pkg *><Py_ssize_t>pkg # or Py_intptr_t > > return Pkg(<object><Py_ssize_t>pkg) > > Note the <Py_ssize_t> cast. When used on a C pointer, it makes a C > integer that Cython convert to python int object. And when <Py_ssize_t> > is used on a python int object, Cyton extracts its integer value > as a C-level value, so it is castable to a C-level pointer. > > Using Py_ssize_t (or Py_intptr_t or your platform intptr_t) guarantees > that the pointer will fit. > > 2) Don't use __cinit__. Declare your own cdef init method and call that. > Since it's cdef method, it can take any C-level arguments, pointerw, > whatever without the need to convert to python objects and back. > > @cython.final # small optimization > cdef _init(self, c_pkg.pkg * pkg): > self._pkg = pkg > > # cdef __cinit__ not needed. Maybe use it to set default > # attribute values. > > cdef Pkg pkg = Pkg.__new__(Pkg) # fast object creation. Pkg() also > works. > pkg._init(pkg) > > (When you use the __new__ trick, __cnit__ is called without > arguments and __init__ is not called at all. The benefit to > this ugly syntax is that __new__ is faster than creating the object > with traditional Pyhton syntax.) > > Also, if all your initialization is pointer assigment, you can > just do it directly: > > cdef Pkg pkg = Pkg.__new__(Pkg) # fast object creation > pkg._pkg = pkg > > > I've chosen to stick with 2) -- I guess I like it better and having an additional _init() is fine with me, makes things clearer. Thanks again! > There is a problem related to cython-dev. I think the code you > wrote should have never compiled in the first place. <PyObject*> > cast must be required if you want to reinterpret a C pointer > as object or vice versa. > > Actually the code compiles just fine and also works as expected :) The only condition is to have Python with debug symbols installed. Any idea why having Python with debug symbols actually overcomes this issue? Thanks again Nikita! Best regards, Marin > > Best regards, > Nikita Nemkin > ______________________________**_________________ > cython-devel mailing list > cython-devel@python.org > http://mail.python.org/**mailman/listinfo/cython-devel<http://mail.python.org/mailman/listinfo/cython-devel> > -- Marin Atanasov Nikolov dnaeon AT gmail DOT com http://www.unix-heaven.org/
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