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

Tim Peters tim.one@comcast.net
Tue, 08 Oct 2002 22🔞46 -0400

[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).