[Python-Dev] Mini-Pep: Simplifying the Integral ABC

[Jeffrey Yasskin]

Because .numerator and .denominator are defined by the Rational ABC,
and Integral inherits from that, removing them from Integral is a
larger change than removing the other methods. You'd have to remove
them from Rational or break the inheritance relation.

Removing the bitwise operators sounds fine to me.

On Wed, Jun 4, 2008 at 1:54 AM, Raymond Hettinger <python at rcn.com> wrote:
> The only comment so far was to keep the __index__ method.
>
> Other than that, is this good to go?
>
> Raymond
>
>
> ----- Original Message -----
>>
>> Target:  Py2.6 and Py3.0
>> Author: Raymond Hettinger
>> Date: May 31, 2008
>>
>> Motivation
>> ----------
>> The principal purpose of an abstract base class is to support multiple
>> implementations of an API; thereby allowing one concrete class to be
>> substitutable for another. This purpose is defeated when useful
>> substitutions
>> are precluded because the ABC is too aggressive in its behavioral
>> requirements
>> -- mandating too many methods, mandating methods that are difficult to
>> implement, or too closely following the full API of a single concrete
>> type.
>>
>> The Integral ABC is somewhat extensive and requires essentially every
>> behavior
>> exhibited by the int concrete class.  Usefully, it provides for basic
>> integer
>> behaviors like simple arithmetic and ordering relations.  However, the
>> current
>> ABC goes beyond that and requires bit-flipping and other operations that
>> are
>> not fundamental to the notion of being an integer.  That makes it
>> challenging
>> to define a new Integral class that isn't already an int.
>>
>> Proposal
>> --------
>> Remove non-essential abstract methods like __index__, three argument
>> __pow__,
>> __lshift__, __rlshift__, __rshift__, __rrshift__, __and__, __rand__,
>> __xor__,
>> __rxor__, __or__, __ror__, and __invert__, numerator, and denominator.
>>
>> Discussion
>> ----------
>> The only known use cases for variants of int are types that limit the
>> range of
>> values to those that fit in a fixed storage width.
>>
>> One existing implementation is in numpy which has types like int0, int8,
>> int16, int32, and int16.  The numpy integral types implement all the
>> methods
>> present in Integral except for the new methods like __trunc__, __index__,
>> real, imag, conjugate, numerator, and denominator.  For the most part,
>> they
>> are fully substitutable into code that expects regular ints; however, they
>> do
>> have wrap-around behaviors such as int8(200)+int8(100) --> int8(44). The
>> wrap-around behaviors make the numpy types totally unsuitable for some
>> applications of Integral such as the fractions module which accepts any
>> integral numerator and denominator.
>>
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-- 
Namasté,
Jeffrey Yasskin
http://jeffrey.yasskin.info/