Numpy C API - Using PyArray_Descr for array creation causes segfaults

Question

I'm trying to use the Numpy C API to create Numpy arrays in C++, wrapped in a utility class. Most things are working as expected, but whenever I try to create an array using one of the functions taking a PyArray_Descr*, the program instantly segfaults. What is the correct way to set up the PyArray_Descr for creation?

An example of code which isn't working:

PyMODINIT_FUNC
PyInit_pysgm()
{
    import_array();
    return PyModule_Create(&pysgmmodule);
}

// ....

static PyAry zerosLike(PyAry const& array)
{
    PyArray_Descr* descr = new PyArray_Descr;
    Py_INCREF(descr); // creation function steals a reference
    descr->type = 'H';
    descr->type_num = NPY_UINT16;
    descr->kind = 'u';
    descr->byteorder = '=';
    descr->alignment = alignof(std::uint16_t);
    descr->elsize = sizeof(std::uint16_t);
    std::vector<npy_intp> shape {array.shape().begin(), array.shape().end()};
    // code segfaults after this line before entering PyAry constructor
    return PyAry(PyArray_Zeros(shape.size(), shape.data(), descr, 0));
}

(testing with uint16).

I'm not setting the typeobj field, which may be the only problem, but I can't work out what the appropriate value of type PyTypeObject would be.

Edit: This page lists the ScalarArray PyTypeObject instances for different types. Adding the line

descr->typeobj = &PyUShortArrType_Type;

has not solved the problem.

n-west · Accepted Answer · 2017-05-09 19:44:22Z

4

Try using

descr = PyArray_DescrFromType(NPY_UINT16);

I've only recently been writing against the numpy C-API, but from what I gather the PyArray_Descr is basically the dtype from python-land. You should building these yourself and use the FromType macro if you can.

answered May 9, 2017 at 19:44

n-west

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Qualia Over a year ago

Whoops - I meant to come back to this - you're right, this is the answer I found.

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