[Cython] Cannot convert pointer to Python Object

[Richard Clarke]

Thank you Robert, the explanation on how and where to use cdef was
most helpful.  I think it has just clicked(with a flag waving
'idiot').

The PyCObject concept is a nice idea, removing cdef foo_t *foo from
outside of __init__ ?  However, I see implications in memory
deallocation.  How does cython currently handle memory deallocation?

I assume the best practice would be for users to deallocate memory in
the class __del__ method (calling the appropriate wrapped c library
destructor).  Otherwise does cython simply free(foo) or interprets the
language to build a depth first deallocation method?  I guess it
should do the simplest free(foo), if the developer was lazy not to
deallocate memory, they can suffer with memory leaks.  I think I might
have answered my own question here...

Richard

On Thu, Jul 23, 2009 at 12:43 PM, Robert
Bradshaw<robertwb at math.washington.edu> wrote:
> On Jul 23, 2009, at 3:39 AM, Richard Clarke wrote:
>
>> Hi,
>>
>> Can anyone point out where I am going wrong?
>
> Sure. There is no way convert a pointer to a Python object. (Perhaps
> we could support this via http://www.python.org/doc/2.6/c-api/
> cobject.html , but certainly that'll take a lot of thought).
>
> You need to make Bar into a cdef class for it to have a foo_t*
> member. Also, if a return type is foo*, you need to make it a cdef
> function. I would recommend reading http://docs.cython.org/ .
>
>> // foo.pyx
>>
>> cdef extern from "foo.h":
>>     ctypedef struct foo_t:
>>         int fd
>>
>>     foo_t* init()
>>
>> class Bar:
>
>  > cdef class Bar:
>  >     cdef foo* __foo
>
>>     def __init__(self):
>>         self.__foo = self.__open()
>>
>>     def __open(self):
>
>  >     cdef foo* open(self):
>
>>         cdef foo_t *foo
>>         foo = init()
>>         return foo
>>
>>
>> Results in the error:
>> /test/foo.pyx:14:12: Cannot convert 'foo_t *' to Python object
>>
>> Cython version 0.9.6.14
>>
>> Thank you,
>> Richard.
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