Unexpected results comparing float to Fraction

[Ian Kelly]

On Mon, Jul 29, 2013 at 9:43 AM, Steven D'Aprano
<steve+comp.lang.python at pearwood.info> wrote:
> Comparing floats to Fractions gives unexpected results:
>
> # Python 3.3
> py> from fractions import Fraction
> py> 1/3 == Fraction(1, 3)
> False
>
> but:
>
> py> 1/3 == float(Fraction(1, 3))
> True
>
>
> I expected that float-to-Fraction comparisons would convert the Fraction
> to a float, but apparently they do the opposite: they convert the float
> to a Fraction:
>
> py> Fraction(1/3)
> Fraction(6004799503160661, 18014398509481984)
>
>
> Am I the only one who is surprised by this? Is there a general rule for
> which way numeric coercions should go when doing such comparisons?

Any float can be precisely represented as a Fraction.  Not so in the
other direction.  So from that standpoint it makes sense to me to cast
to Fraction when comparing.