[Python-Dev] Re: PEP239 (Rational Numbers) Reference Implementation and new issues

[Tim Peters]

[Guido, on 3/5r]
> I'd like at least one of those return '0.6' or '0.6r'.

[Oren Tirosh]
> Why should any of them go through a potetially lossy transformation?

0.6r is exact, although it's hard to know whether Guido was hoping to
preserve that or not.

> If you need to approximate a ratio as a finite decimal fraction it should
> be explicit: str(float(r)).
> I think it will also make a good visual cue to always use
> rational notation  for rationals and decimal fractions for floats.

The trailing 'r' *is* rational notation, and stuff like this probably isn't
a good idea for str():

> #e6.02e-45
301/50000000000000000000000000000000000000000000000
>

6.02e-45r would be clearer to virtually anyone.

> (+ 312 (/ 1 3))
937/3
>

would likely be clearer to virtually anyone as 312+1/3r too.

But most of all, I agree that if you're working with rationals, you don't
want to lose information silently, not even in a "pleasant" string.

> The result of repr() should eval() back to exactly the same object. The
> result of str() should be the 'pretty' representation because this is the
> form displayed by print statements and %s formatting. I find
> '2/3' prettier than '0.666666666667'

2/3r works for both for me.  0.666...7 doesn't work for me at all as a
stringification of a rational (if I want to approximate, I'll ask for an
approximation).