Two issues with sip.array

[Ognyan Moore]

Hi Phil,

We have identified two issues with sip.array and I think we identified
their respective fixes too.

The first has to do with the buffer protocol, we have a work-around but
here is some code to demonstrate the issue:

from PyQt6 import QtCore, sip
import numpy as np


LEN = 5
sa = sip.array(QtCore.QLineF, LEN)   # LEN * 4 doubles
assert len(sa) == LEN


# following fails due to wrong size
# memory = np.frombuffer(sa, dtype=np.float64)
# ValueError: buffer size must be a multiple of element size


vp = sip.voidptr(sa)
print(f'expecting {LEN*4*8}, got {vp.getsize()}')


# the following is our workaround
vp.setsize(len(sa)*4*8)
memory = np.frombuffer(vp, dtype=np.float64)
assert len(memory) == LEN * 4

The bug is in sip_array.c
# static int sipArray_getbuffer(PyObject self, Py_bufferview, int flags)
#    view->len = array->len;
# should be
#    view->len = array->len * array->stride;
# https://docs.python.org/3/c-api/buffer.html#c.PyObject_GetBuffer

The second issue is that slicing sip.array does not work:

from PyQt6 import QtCore, sip


sa1 = sip.array(QtCore.QLineF, 10)
assert len(sa1) == 10
sa2 = sa1[2:8]
assert len(sa2) == 6


vp1 = sip.voidptr(sa1)
assert int(vp1) != 0
vp2 = sip.voidptr(sa2)
print(hex(int(vp2)))    # NULL pointer

The behavior we would expect is that slicing would yield a non-owning
memory view.

The bug is also in sip_array.c
# static PyObject sipArray_subscript(PyObjectself, PyObject *key)
#   element(array->data, start)
# should be
#   element(array, start)

Thanks Phil!
Ogi
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