[Python-Dev] [Python-checkins] peps: Pre-alpha draft for PEP 435 (enum). The name is not important at the moment, as (original) (raw)

Terry Reedy tjreedy at udel.edu
Tue Feb 26 16:01:21 CET 2013

On 2/25/2013 6:53 PM, Greg Ewing wrote:

Barry Warsaw wrote:

>>> Colors = make('Colors', 'red green blue'.split()) >>> Animals = make('Animals', 'ant bee cat'.split()) >>> Colors.green == Animals.bee The currently suggested solution to that seems to be to make comparison non-transitive, so that Colors.green == 1 and Animals.bee == 1 but Colors.green != Animals.bee. And then hope that this does not create a quantum black hole that sucks us all into a logical singularity...

But it will;-). To repeat myself, transitivity of equality is basic to thought, logic, and sets and we should not deliver Python with it broken. (The non-reflexivity of NAN is a different issue, but NANs are intentionally insane.)

Decimal(0) == 0 == 0.0 != Decimal(0) != Fraction(0) == 0 was a problem we finally fixed by making integer-valued decimals compare equal to the same valued floats and fractions. In 3.3:

from decimal import Decimal as D from fractions import Fraction as F 0 == 0.0 == D(0) == F(0) True

http://bugs.python.org/issue4087 http://bugs.python.org/issue4090 explain the practical problems. We should NOT knowingly go down this road again. If color and animal are isolated from each other, they should each be isolated from everything, including int.

-- Terry Jan Reedy

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