On 28/09/18 10:25, Matti Picus wrote:
Breaking this into a number of sub-dsicussions, since we seem to be
branching. The original topic was
Re: [Cython] Enhancing "ctyepdef class numpy.ndarray" with getter
properties
On 28/09/18 01:20, Robert Bradshaw wrote:
Hmm...so in this case it upgrading Cython would cause an
unconditional switch from direct access to a function call without
any code change (or choice) for users of numpy.pxd. I am curious what
kind of a slowdown this would represent (though would assume this
kind of analysis was done by the NumPy folks when choosing macro vs.
function for the public API).
As I point out in the "experiment" comment referenced above,
pandas has
code that needs lvalue access to ndarray data, so they would be
stuck
with the old API which is deprecated but still works for now.
Scipy has
no such code and oculd move forward to the newer API.
But if we upgraded Cython, how would they access the old API? I
suppose they could create a setter macro of their own to use in the
(presumably few) cases where they needed an lvalue.
- Robert
NumPy changed its recommended API to an opaque one via inline getter
functions in 2011, in this PR https://github.com/numpy/numpy/pull/116.
I could not find a discussion on performance impact, perhaps since the
functions are in the header files and marked inline. Hopefully the
compilers will properly deal with making them fast. However, it is
true that when people update to a new version of a library things
change. In this case, there are backward-compatibility macros that
revert the post-1.7 functions into pre-1.7 macros with the same name.
Thus for the experiment I used a new numpy.pxd, defined the pre-1.7
api in the pandas build (experimental changeset
https://github.com/mattip/pandas/commit/9113bf7e55e1eddece3544c1ad3ef2a761b5210a),
and was still able to access ndarray.data as a lvalue.
Matti
This means cython/numpy could provide an integration path based on numpy
starting to ship its own numpy.pxd:
- Cython would define the macro (if not already defined) to use the
pre-1.7 Numpy API in the numpy.pxd it ships. This would still work
(lvalues would be allowed) after direct access is replaced with the
getter properties, since they are macros
- NumPy would define the macro to use post-1.7 API (if not already
defined) in the numpy.pxd it ships, which as I understand would take
precedence over cython's. Then projects like pandas could freely upgrade
Cython without changing their codebase, but would encounter errors when
updating NumPy.
Matti
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