Hi!
I am sure that the following problem has a solution that is well-known
- but not well-known to me, and also I did not succeed in googling it.
Background is #12029.
In the following, self is a ClonableIntArray, but I guess the problem
is more general. self._list is some "int *" array of known length
self._len. The aim is to convert self._list into a Python list, as
quickly as possible.
Is there a ready-made function that would do such conversion?
I did this, which works fine:
cdef int i
cdef list L = []
for i from 0<=i<self._len:
L.append(self._list[i])
return L
But Florent was suggesting that it might be faster to create an
"empty" list of length self._len using PyList_New, and to put the
items onto that list by PyList_SetItem, rather than appending them.
First question: Could PyList_SET_ITEM (for a list of known length)
really be faster than appending to the list?
Second question: I know that PyList_SET_ITEM is only borrowing a
reference. Hence, I am not surprised that I got segfaults in the first
place. But why am I still getting segfaults with the following code,
where I manually add a reference?
cdef int i, o
cdef list L = PyList_New(self._len)
for i from 0<=i<self._len:
o = self._list[i]
Py_INCREF(o)
PyList_SET_ITEM(L,i,o)
return L
More precisely, it works (or seems to work) on ClonableIntArrays of
size 100, but not on a list of size 500.
Best regards,
Simon
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