On 02/02/2012 10:16 PM, mark florisson wrote:
On 2 February 2012 12:19, Dag Sverre Seljebotn
<d.s.seljeb...@astro.uio.no> wrote:
I just realized that
cdef int[:] a = None
raises an exception; even though I'd argue that 'a' is of the "reference"
kind of type where Cython usually allow None (i.e., "cdef MyClass b = None"
is allowed even if type(None) is NoneType). Is this a bug or not, and is it
possible to do something about it?
Dag Sverre
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Yeah I disabled that quite early. It was supposed to be working but
gave a lot of trouble in cases (segfaults, mainly). At the time I was
trying to get rid of all the segfaults and get the basic functionality
working, so I disabled it. Personally, I have never liked how things
Well, you can segfault quite easily with
cdef MyClass a = None
print a.field
so it doesn't make sense to slices different from cdef classes IMO.
can be None unchecked. I personally prefer to write
cdef foo(obj=None):
cdef int[:] a
if obj is None:
obj = ...
a = obj
Often you forget to write 'not None' when declaring the parameter (and
apparently that it only allowed for 'def' functions).
As such, I never bothered to re-enable it. However, it does support
control flow with uninitialized slices, and will raise an error if it
is uninitialized. Do we want this behaviour (e.g. for consistency)?
When in doubt, go for consistency. So +1 for that reason. I do believe
that setting stuff to None is rather vital in Python.
What I typically do is more like this:
def f(double[:] input, double[:] out=None):
if out is None:
out = np.empty_like(input)
...
Having to use another variable name is a bit of a pain. (Come on -- do
you use "a" in real code? What do you actually call "the other obj"? I
sometimes end up with "out_" and so on, but it creates smelly code quite
quickly.)
It's easy to segfault with cdef classes anyway, so decent nonechecking
should be implemented at some point, and then memoryviews would use the
same mechanisms. Java has decent null-checking...
Dag Sverre
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