c malloc array pointer return in cython

Question

How does one to return a malloc array pointer (or numpy array pointer) in cython back to python3, efficiently.

The cython code works perfectly as long as I don\'t re

Answer 1

Numpy C API

Your question is similar to this post.

You can use the function below to pass a C pointer to Numpy array. The memory will be freed automatically when the Numpy array is recycled. If you want free the pointer mamully, you should not set NPY_OWNDATA flag.

import numpy as np
cimport numpy as np

cdef pointer_to_numpy_array_complex128(void * ptr, np.npy_intp size):
    '''Convert c pointer to numpy array.
    The memory will be freed as soon as the ndarray is deallocated.
    '''
    cdef extern from "numpy/arrayobject.h":
        void PyArray_ENABLEFLAGS(np.ndarray arr, int flags)
    cdef np.ndarray[np.complex128, ndim=1] arr = \
            np.PyArray_SimpleNewFromData(1, &size, np.NPY_COMPLEX128, ptr)
    PyArray_ENABLEFLAGS(arr, np.NPY_OWNDATA)
    return arr

For reference:

• PyArray_SimpleNewFromData
• Numpy Data Type API

Cython Typed Memoryviews

Of couse, you can also use cython memoryview.

import numpy as np
cimport numpy as np

cdef np.complex128_t[:,:] view =  c_pointer
numpy_arr = np.asarray(view)

The code above will transfer C pointer to a numpy array. However this would not free memory automaticlly, you have to free the memory by yourself or it would lead to memory leak!