Re: Storing a C pointer in a Python class instance
Carl Banks pavlovevide...@gmail.com wrote in message news:d50bba1e-b272-4e39-8a58-377531278...@z4g2000prh.googlegroups.com... On Sep 30, 5:24 am, lallous lall...@lgwm.org wrote: Hello After using the PyCObject, I cannot pickle the class anymore. Any simple solution to this problem? (or resorting to __reduce__ is the only solution?) You can't pickle a CObject, you'd have to create a custom type (one that implements one of the pickling methods) for that. Or arrange for whatever object contains the CObject to pack and unpack it manually. Out of curiosity, what kind of data you storing in this CObject? Maybe we can help you choose a better way to handle it at the C level. I am wrapping a C++ pointer with the python object. That way I can tell with which C++ object a given python class instance is associated. The thing is when developing, I need to pickle but I don't need the C++ pointer, so I solved the problem with conditional compilation: - testing: pickle allowed and This is stored in the py object - production code: no need to pickle and this and pyobject are bound Thanks, Elias -- http://mail.python.org/mailman/listinfo/python-list
Re: Storing a C pointer in a Python class instance
Thanks everyone. Finally, I used Falcolas suggestion and took into consideration sturlamolden's comments. Regards, Elias lallous lall...@lgwm.org wrote in message news:h9sgcn$iv...@aioe.org... Hello From my C extension module I want to store a C pointer in a given PyObject. The only way I figure how to do it is to use Py_BuildValues and store the poiner casted to Py_ssize_t, thus: Py_BuildValues(n, (Py_ssize_t)my_ptr) Can it be done differently? Regards, Elias -- http://mail.python.org/mailman/listinfo/python-list
Re: Storing a C pointer in a Python class instance
Hello After using the PyCObject, I cannot pickle the class anymore. Any simple solution to this problem? (or resorting to __reduce__ is the only solution?) Thanks, Elias Falcolas garri...@gmail.com wrote in message news:9d3790aa-f7d9-4bb5-a81f-5428b2d60...@v25g2000yqk.googlegroups.com... On Sep 29, 2:27 am, lallous lall...@lgwm.org wrote: Hello From my C extension module I want to store a C pointer in a given PyObject. The only way I figure how to do it is to use Py_BuildValues and store the poiner casted to Py_ssize_t, thus: Py_BuildValues(n, (Py_ssize_t)my_ptr) Can it be done differently? Regards, Elias You can use a PyCObject_FromVoidPtr http://docs.python.org/c-api/cobject.html PyArg_ParseTuple(args, O, pyVoidPointer); castPointer = (type *) PyCObject_AsVoidPtr(pyVoidPointer); return PyCObject_FromVoidPtr((void *) castPointer, NULL); -- http://mail.python.org/mailman/listinfo/python-list
Re: Storing a C pointer in a Python class instance
On Sep 30, 5:24 am, lallous lall...@lgwm.org wrote: Hello After using the PyCObject, I cannot pickle the class anymore. Any simple solution to this problem? (or resorting to __reduce__ is the only solution?) You can't pickle a CObject, you'd have to create a custom type (one that implements one of the pickling methods) for that. Or arrange for whatever object contains the CObject to pack and unpack it manually. Out of curiosity, what kind of data you storing in this CObject? Maybe we can help you choose a better way to handle it at the C level. Carl Banks -- http://mail.python.org/mailman/listinfo/python-list
Re: Storing a C pointer in a Python class instance
On Sep 29, 11:16 am, sturlamolden sturlamol...@yahoo.no wrote: On 29 Sep, 19:11, Carl Banks pavlovevide...@gmail.com wrote: CObjects can be passed a C function as a deallocator; this should work as reliably as a custom class deallocator. Except that __del__ prevents cyclic GC. You are mistaken on two counts. First of all, a CObject is not a container. It can't prevent cyclic GC because it's never a part of a cycle. Second, CObjects do not have a __del__ method. They call the supplied constructor from the type's tp_dealloc slot. Use of the tp_dealloc slot does not, by itself, prevent cyclic GC. Bottom line is, the CObject's deallocator is as reliable as a custom type's tp_dealloc. Carl Banks -- http://mail.python.org/mailman/listinfo/python-list
Re: Storing a C pointer in a Python class instance
On 30 Sep, 19:03, Carl Banks pavlovevide...@gmail.com wrote: Second, CObjects do not have a __del__ method. They call the supplied constructor from the type's tp_dealloc slot. Use of the tp_dealloc slot does not, by itself, prevent cyclic GC. Bottom line is, the CObject's deallocator is as reliable as a custom type's tp_dealloc. You are right. I did not look at the PyCObject_* API close enough. I thought of wrapping the CObject with a Python class, and calling the destructor from __del__. That would be less reliable. S.M. -- http://mail.python.org/mailman/listinfo/python-list
Storing a C pointer in a Python class instance
Hello From my C extension module I want to store a C pointer in a given PyObject. The only way I figure how to do it is to use Py_BuildValues and store the poiner casted to Py_ssize_t, thus: Py_BuildValues(n, (Py_ssize_t)my_ptr) Can it be done differently? Regards, Elias -- http://mail.python.org/mailman/listinfo/python-list
Re: Storing a C pointer in a Python class instance
On Sep 29, 2:27 am, lallous lall...@lgwm.org wrote: Hello From my C extension module I want to store a C pointer in a given PyObject. The only way I figure how to do it is to use Py_BuildValues and store the poiner casted to Py_ssize_t, thus: Py_BuildValues(n, (Py_ssize_t)my_ptr) Can it be done differently? Regards, Elias You can use a PyCObject_FromVoidPtr http://docs.python.org/c-api/cobject.html PyArg_ParseTuple(args, O, pyVoidPointer); castPointer = (type *) PyCObject_AsVoidPtr(pyVoidPointer); return PyCObject_FromVoidPtr((void *) castPointer, NULL); -- http://mail.python.org/mailman/listinfo/python-list
Re: Storing a C pointer in a Python class instance
On 29 Sep, 10:27, lallous lall...@lgwm.org wrote: Hello From my C extension module I want to store a C pointer in a given PyObject. The only way I figure how to do it is to use Py_BuildValues and store the poiner casted to Py_ssize_t, Formally, you should cast the pointer to Py_intptr_t, as it has the same size as void*. Py_ssize_t has the same size as size_t, but the C standard does not mandate that sizeof(void*) == sizeof(size_t). In fact there are segment and offset architectures where this is not true. Casting a pointer to Py_ssize_t accidentally works if you have a flat address space. Can it be done differently? You can use PyCObject, or write your own extension type that wraps the pointer (very easy to to with Cython or Pyrex). The advantage of using an extension type is you have a guarantee from Python on the deallocator method being called (cdef __dealloc__ in Cython). If the pointer references a resource that needs to be closed, this is safer than using a __del__ method in a Python class. -- http://mail.python.org/mailman/listinfo/python-list
Re: Storing a C pointer in a Python class instance
On Sep 29, 9:42 am, sturlamolden sturlamol...@yahoo.no wrote: You can use PyCObject, or write your own extension type that wraps the pointer (very easy to to with Cython or Pyrex). The advantage of using an extension type is you have a guarantee from Python on the deallocator method being called (cdef __dealloc__ in Cython). CObjects can be passed a C function as a deallocator; this should work as reliably as a custom class deallocator. Carl Banks -- http://mail.python.org/mailman/listinfo/python-list
Re: Storing a C pointer in a Python class instance
On 29 Sep, 19:11, Carl Banks pavlovevide...@gmail.com wrote: CObjects can be passed a C function as a deallocator; this should work as reliably as a custom class deallocator. Carl Banks Except that __del__ prevents cyclic GC. -- http://mail.python.org/mailman/listinfo/python-list
