On Thu, 07 Mar 2013 17:16:10 +0600, Yury V. Zaytsev <y...@shurup.com>
wrote:
Hi,
Is there any syntax that I can use to do something like this in Cython:
py_object_ = PyList_New(123); ?
If not, do you think that this can be added in one way or another?
Unfortunately, I can't think of a non-disruptive way of doing it. For
instance, if this
[None] * N
is given a completely new meaning, like make an empty list (of NULLs),
instead of making a real list of Nones, it will certainly break Python
code. Besides, it would probably be still faster than no pre-allocation,
but slower than an empty list with pre-allocation...
Maybe
[NULL] * N ?
Any ideas?
I really like the "[NULL] * N" thing.
Efficient empty list allocation and filling is something I stumble upon
quite often, especially in binding code.
I doubt Cython will be able to automatically use PyList_SET_ITEM
for assignment to such NULL list (it would require induction variable
analysis), but eliminating one extra pass over the list is already helpful.
Implementation note (if this gets implemented):
Cython's optimized list assignment routine uses Py_DECREF, this will
have to be changed to Py_XDECREF, otherwise NULL list items won't be
directly assignable from Cython.
(PyList_SetItem always uses Py_XDECREF on the old element).
What do you need it for?
Won't list comprehensions work for you? They could potentially be adapted
to presize the list.
List comprehensions do not preallocate the list.
If they did, the need for the above would be somewhat diminished.
And why won't [None]*N help you out? It should be pretty cheap.
[None] * N makes
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