On Mon, Nov 14, 2011 at 02:54:19PM -0800, Simon King wrote: > 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.
For the record, I think I answered all of this on #12029. Cheers, Florent -- To post to this group, send an email to sage-devel@googlegroups.com To unsubscribe from this group, send an email to sage-devel+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-devel URL: http://www.sagemath.org
