[Cython] Bindings performance issue

[mark florisson]

On 2 June 2011 23:59, Robert Bradshaw <robertwb at math.washington.edu> wrote:
> On Thu, Jun 2, 2011 at 2:45 PM, mark florisson
> <markflorisson88 at gmail.com> wrote:
>> On 2 June 2011 23:34, Robert Bradshaw <robertwb at math.washington.edu> wrote:
>>> On Thu, Jun 2, 2011 at 2:21 PM, mark florisson
>>> <markflorisson88 at gmail.com> wrote:
>>>> On 2 June 2011 23:13, Robert Bradshaw <robertwb at math.washington.edu> wrote:
>>>>> On Thu, Jun 2, 2011 at 2:03 PM, mark florisson
>>>>> <markflorisson88 at gmail.com> wrote:
>>>>>
>>>>>>>>> If anyone is assigning a Cython function to an object and then using
>>>>>>>>> it they're counting on the current non-binding behavior, and it will
>>>>>>>>> break. The speed is probably a lesser issue, which is what benchmarks
>>>>>>>>> are for.
>>>>>>>>
>>>>>>>> If you're binding functions to classes without expecting it to ever
>>>>>>>> bind, you don't really have bitching rights when stuff breaks later
>>>>>>>> on. You should have been using staticmethod() to begin with. And we
>>>>>>>> never said that our functions would never bind :)
>>>>>>>
>>>>>>> No, you're assigning it to an object, counting on being able to call
>>>>>>> it later on. E.g. the following is legal (though contrived in this
>>>>>>> example):
>>>>>>>
>>>>>>> sage: class A:
>>>>>>> ....:     pass
>>>>>>> ....:
>>>>>>> sage: a = A()
>>>>>>> sage: a.foo = max
>>>>>>> sage: a.foo([1,2,3])
>>>>>>> 3
>>>>>>>
>>>>>>> If instead of len, it was one of our functions, then it would be bad
>>>>>>> to suddenly change the semantics, because it could still run but
>>>>>>> produce bad answers (e.g. if we had implemented max, suddenly a would
>>>>>>> be included in the comparison). This is why I proposed raising an
>>>>>>> explicit error as an intermediate step.
>>>>>>>
>>>>>>> If we don't promise anything, the contract is whatever the code does.
>>>>>>> That's the problem with not having a specification (which would be
>>>>>>> really nice, but is a lot of work).
>>>>>>
>>>>>> Functions on objects never get bound, they only get bound if they are
>>>>>> on the class. So your code would still work with binding functions.
>>>>>
>>>>> True. It would still break "A.foo = max" though. I'm not saying we
>>>>> should support or encourage this, but lets break it hard before we
>>>>> break it subtly.
>>>>
>>>> Again, such code is highly fragile and frankly incorrect to begin
>>>> with, as it's based on the assumption that "Cython functions" never
>>>> get bound.
>>>
>>> I agree, but I bet there's code out there depending on it, in
>>> particular workarounds for our current broken semantics will
>>> themselves break.
>>
>> Workarounds wouldn't break, as they would wrap the non-binding
>> function in another object, and implement __get__ to return a new
>> object that, when called, would call the original function with 'self'
>> as the first argument.
>
> Depends on the workaround. I'm thinking workarounds like "oh, self
> isn't getting passed, guess I'll have to pass it manually here..."

Ah, something like functools.partial. Yeah, that'd break :)

>>>> Getting functions (defined outside of class bodies) to bind
>>>> in classes is a feature, I sometimes found myself to want it. So
>>>> basically an error would be fine, but it would prevent normal usage as
>>>> we have it in Python.
>>>
>>> The error would just be for a transition period.
>>
>> The transition period would be for an entire release?
>
> Yes, though hopefully a much shorter release cycle than this last one.
> I just haven't had time to fix those remaining failing Sage tests, and
> we keep merging in more and more stuff (which is good, but we're well
> overdue for a release by now.)

Ok. Then perhaps it would be better to merge the support for fused
types in the next release? I won't be available until the 6th of July
for coding, so until then we'd be stuck with cython.fused_type() in a
ctypedef.

> - Robert
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