PEP239 (Rational Numbers) Reference Implementation and new issues

Paul Rubin phr-n2002b at NOSPAMnightsong.com
Thu Oct 3 01:20:35 CEST 2002


python-pep at ccraig.org writes:
> 1) Should future division return rationals rather than floats.  I had
> sort of assumed this would happen, but I just had a discussion with
> Kirby Urner and couldn't convince him it was a good idea, so I guess
> it isn't so clear.

No--on the theory that 3/2 == 1.5 in future division for the benefit
of newbies who get confused by 3/2 == 1 as we're used to from int
arithmetic.  Future division returns floats because that's what
non-programmers are used to from BASIC and spreadsheets.  They
don't expect rationals, so rationals aren't the right thing.

> 2) Should floats compare equal with rationals only when they are
> equal, or whenever the are the closest float?  (i.e. will .2 
> compare equal to rational(1, 5))
> 
> 3) Should rationals try to hash the same as floats?  My leaning on
> this is that it will be decided by (2).  If they compare equal when
> 'close enough' then they should hash the same, if not then they should
> only hash the same when both are integral.  I would rather not see .5
> hash with rational(1, 2) but not .2 with rational(1, 5).

Unless there's a good reason to do something different, follow existing
standards, e.g. do what Scheme or Common Lisp does in these situations.



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