On 2022-03-12 21:24, Jen Kris via Python-list wrote:
I have a C API project where I have to slice a list into two parts.
Unfortunately the documentation on the slice objects is not clear enough for me
to understand how to do this, and I haven’t found enough useful info through
research. The list contains tuple records where each tuple consists of a
dictionary object and a string.
The relevant part of the Python code is:
half_slice = int(len(dictdata) * 0.5)
subdata_a = dictdata[half_slice:]
subdata_b = dictdata[:half_slice]
This is what I’ve done so far with the C API:
int64_t Calc_Slices(PyObject* pDictdata, int64_t records_count)
{
long round_half = records_count * 0.5;
PyObject* half_slice = PyLong_FromLong(round_half);
PyObject* slice = PySlice_New(PyLong_FromLong(0), half_slice, 0);
PyObject* subdata_a = PyObject_GetItem(pDictddata, slice);
return 0;
}
On the final line (subdata_a) I get a segfault. I know that the second
parameter of PyObject_GetItem is a “key” and I suspect that’s where the
problem comes from, but I don’t understand what a key is in this context.
The code shown above omits error handling but none of the objects leading up to
the final line is null, they all succeed.
Thanks for any ideas.
Use PySequence_GetSlice to slice the list.
Also, why use floats when you can use integers?
long round_half = records_count / 2;
(In Python that would be half_slice = len(dictdata) // 2.)
--
https://mail.python.org/mailman/listinfo/python-list
