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

[Antoine Pitrou]

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.

Regards

Antoine.