On 5 February 2012 22:03, mark florisson <markflorisso...@gmail.com> wrote: > On 2 February 2012 21:38, Dag Sverre Seljebotn > <d.s.seljeb...@astro.uio.no> wrote: >> 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 >>>> _______________________________________________ >>>> cython-devel mailing list >>>> cython-devel@python.org >>>> http://mail.python.org/mailman/listinfo/cython-devel >>> >>> >>> 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. > > Yeah I think we should go back to this discussion :) Checking for None > and allowing slices to be None is simply very convenient, and doesn't > involve any drastic changes. I was never really against it, I just > never got around to implementing it.
We should now be able to use None memoryview slices: https://github.com/markflorisson88/cython/commit/a24495ac1348926af5e085334c4e6a960e723f87 They also coerce back to None when coercing to object. >> 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 >> _______________________________________________ >> cython-devel mailing list >> cython-devel@python.org >> http://mail.python.org/mailman/listinfo/cython-devel _______________________________________________ cython-devel mailing list cython-devel@python.org http://mail.python.org/mailman/listinfo/cython-devel
