[Cython] Bindings performance issue

[Robert Bradshaw]

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..."

>>> 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.)

- Robert