AFAIK, you only have to INCREF the dtype. And only for numpy array creation routines that take a dtype object as an argument (they "steal" a dtype reference, which is why you have to incref it).
On Sun, Nov 15, 2009 at 2:09 AM, Matthew Brett <matthew.br...@gmail.com> wrote: > Hi, > > I've been spending some time with Cython in Scipy: > http://projects.scipy.org/scipy/browser/trunk/scipy/io/matlab > > In general, it's been very enjoyable - a warm thank you to y'all for > making it so clear and so useful. > > Here, I just wanted to check that I had understood the idioms right to > call the numpy C-API. I'm doing this for speed. > > Imagine I have a string 'data', length 'n' bytes, and a numpy dtype > 'dt', and I wanted to make a 1d array. In python that is: > > arr = np.ndarray(shape=(n,), dtype=dt, buffer=data) > > Am I right, that in Cython, this would be a function like the > following (that does work): > > # start of make_array.pyx > from python cimport Py_INCREF > > cdef extern from "Python.h": > ctypedef struct PyTypeObject: > pass > > import numpy as np > cimport numpy as cnp > > cdef extern from "numpy/arrayobject.h": > PyTypeObject PyArray_Type > object PyArray_NewFromDescr(PyTypeObject *subtype, > cnp.dtype newdtype, > int nd, > cnp.npy_intp* dims, > cnp.npy_intp* strides, > void* data, > int flags, > object parent) > > cdef extern from "workaround.h": > void PyArray_Set_BASE(cnp.ndarray arr, object obj) > > # NOTE: numpy MUST be initialized before any other code is executed. > cnp.import_array() > > > def make_1d_array(cnp.npy_intp size, object data, cnp.dtype dt): > cdef char *ptr > ptr = data > Py_INCREF(<object> dt) > Py_INCREF(<object> data) > narr = PyArray_NewFromDescr(&PyArray_Type, > dt, > 1, > &size, > NULL, > <void *>ptr, > 0, > <object>NULL) > PyArray_Set_BASE(narr, data) > return narr > # end of make_array.pyx > > where 'workaround.h' (thanks to Dag Sverre) [1]: > > #include <numpy/arrayobject.h> > #define PyArray_Set_BASE(arr, obj) PyArray_BASE(arr) = obj > > Is that correct? In particular, I don't think I fully understand the > right idiom for using the numpy array type PyArray_Type. Did I > understand correctly that I have to Py_INCREF both the dtype and the > data? [2] [3] > > Many thanks for any help. > > Matthew > > [1] http://codespeak.net/pipermail/cython-dev/2009-June/005979.html > [2] http://docs.scipy.org/doc/numpy/reference/c-api.array.html > [3] http://wiki.cython.org/tutorials/numpy#UsingtheNumpyCAPI > _______________________________________________ > Cython-dev mailing list > Cython-dev@codespeak.net > http://codespeak.net/mailman/listinfo/cython-dev > _______________________________________________ Cython-dev mailing list Cython-dev@codespeak.net http://codespeak.net/mailman/listinfo/cython-dev
