On 29/07/2013 17:20, Chris Angelico wrote:
On Mon, Jul 29, 2013 at 5:09 PM, MRAB <pyt...@mrabarnett.plus.com> wrote:
I'm surprised that Fraction(1/3) != Fraction(1, 3); after all, floats
are approximate anyway, and the float value 1/3 is more likely to be
Fraction(1, 3) than Fraction(6004799503160661, 18014398509481984).
At what point should it become Fraction(1, 3)?
Fraction(0.3)
Fraction(5404319552844595, 18014398509481984)
Fraction(0.33)
Fraction(5944751508129055, 18014398509481984)
Fraction(0.333)
Fraction(5998794703657501, 18014398509481984)
Fraction(0.3333333)
Fraction(6004798902680711, 18014398509481984)
Fraction(0.3333333333)
Fraction(6004799502560181, 18014398509481984)
Fraction(0.3333333333333)
Fraction(6004799503160061, 18014398509481984)
Fraction(0.33333333333333333)
Fraction(6004799503160661, 18014398509481984)
Rounding off like that is a job for a cool library function (one of
which was mentioned on this list a little while ago, I believe), but
not IMO for the Fraction constructor.
How about this?
>>> from fractions import Fraction
>>> help(Fraction.limit_denominator)
Help on function limit_denominator in module fractions:
limit_denominator(self, max_denominator=1000000)
Closest Fraction to self with denominator at most max_denominator.
>>> Fraction('3.141592653589793').limit_denominator(10)
Fraction(22, 7)
>>> Fraction('3.141592653589793').limit_denominator(100)
Fraction(311, 99)
>>> Fraction(4321, 8765).limit_denominator(10000)
Fraction(4321, 8765)
>>> Fraction(1/3).limit_denominator()
Fraction(1, 3)
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