Unexpected results comparing float to Fraction
Serhiy Storchaka
storchaka at gmail.com
Mon Jul 29 21:34:04 CEST 2013
29.07.13 19:09, MRAB написав(ла):
> 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).
>>> def approximate_fraction(f):
prev_numer, numer = 0, 1
prev_denom, denom = 1, 0
r = f
while True:
i = math.floor(r)
prev_numer, numer = numer, i * numer + prev_numer
prev_denom, denom = denom, i * denom + prev_denom
if i == r or numer / denom == f:
break
r = 1 / (r - i)
return Fraction(numer, denom)
>>> approximate_fraction(1/3)
Fraction(1, 3)
>>> approximate_fraction(1e-17)
Fraction(1, 100000000000000000)
>>> approximate_fraction(math.pi)
Fraction(245850922, 78256779)
I guess the Fraction constructor is more faster than this function.
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