[Python-ideas] Add additional special method lookups to math module

[Case Van Horsen]

On Wed, Nov 9, 2011 at 5:01 PM, Antoine Pitrou <solipsis at pitrou.net> wrote:
> On Wed, 9 Nov 2011 16:55:16 -0800
> Case Van Horsen <casevh at gmail.com> wrote:
>
>> On Wed, Nov 9, 2011 at 3:02 PM, Steven D'Aprano <steve at pearwood.info> wrote:
>> > Case Van Horsen wrote:
>> >>
>> >> Currently the functions round(), math.ceil(), math.floor(), and
>> >> math.trunc() all check for the existence of a special method
>> >> (__round__, __ceil__, __floor__, and __trunc__). Would it be possible
>> >> to enhance the math and cmath modules to check for the existence of a
>> >> special method for (almost) functions? For example, math.sin(obj)
>> >> would first check for obj.__sin__.
>> >
>> > I would not object to this.
>> >
>> > The only function I can honestly say I have had a concrete use-case for is
>> > math.sqrt. This comes up from time to time, e.g.:
>> >
>> > http://bytes.com/topic/python/answers/463861-how-overload-sqrt-module
>> > http://permalink.gmane.org/gmane.comp.python.general/694849
>> >
>> > However, how far should we go? Does every function in the math module
>> > require a dunder method, e.g. __degrees__ ? What happens if we add more
>> > functions, say math.bessel? Do we really expect that all numeric types must
>> > support a __bessel__ method? I suspect that this proposal is actually bigger
>> > than it seems at first glance.
>>
>> It would be completely optional for a numeric type to support these
>> methods. If they're not supported, the numeric type is converted to a
>> float and then math.function proceeds as it currently does.
>>
>> >
>> > We can:
>> >
>> > * Do nothing (the status quo). If you write a numeric type, you can support
>> > a small number of mathematical operations, such as + and math.floor, but not
>> > others, such as math.sqrt or math.sin.
>> >
>> > * Officially recommend that people monkey-patch the math module if they want
>> > to write a drop-in replacement for numeric types. I consider this
>> > unspeakable, but mention it for completeness since others have raised the
>> > possibility.
>> >
>> > * Add support for dunder methods in an ad hoc manner, when and as requested,
>> > without making any promises about any other functions.
>>
>> I hacked mathmodule.c FUNC1 macro to perform the lookup the many of
>> math module functions. It was only about 15 lines of code (but it
>> doesn't check if NotImplemented is returned.) Unfortunately, it
>> increases the running time of math.sin, for example, by 15%. I need to
>> look at the Identifier API to see if that helps the performance but I
>> don't think 15% is a penalty everyone should pay.
>
> You can special-case floats using PyFloat_CheckExact and see if that
> helps.

Thanks. That decreases the penalty to about 1.5%. I'll finish hacking
mathmodule.c and gmpy2 and run some additional tests.

casevh
>
> Regards
>
> Antoine.
>
>
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