I'd like to compute the Greatest Common Divisor of two rational numbers implemented as fractions.Fraction instances. It works as expected although deprecation warning is printed:
In [1]: gcd(Fraction(2, 3), Fraction(2, 3))
/usr/local/bin/ipython:1: DeprecationWarning: fractions.gcd() is deprecated. Use math.gcd() instead.
#!/usr/local/opt/python3/bin/python3.6
Out[1]: Fraction(1, 6)
Looking at the documentation I can see that fractions.gcd() is indeed deprecated and that users are invited to use math.gcd() instead. The problem is that the latter does not support rational numbers:
In [2]: gcd(Fraction(2, 3), Fraction(2, 3))
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
<ipython-input-2-c3ad2389f290> in <module>()
----> 1 gcd(Fraction(2, 3), Fraction(2, 3))
TypeError: 'Fraction' object cannot be interpreted as an integer
Which function can I use in replacement of fractions.gcd()? I'm not looking for the actual algorithm used here, but the replacement for the deprecated function.
You might have to write one. gcd(a/b, c/d) = gcd(a, c)/lcm(b, d), so this isn't too bad. math doesn't provide a lcm, so I'm using the one written here.
from fractions import Fraction
from math import gcd
def lcm(a, b):
"""Return lowest common multiple."""
return a * b // gcd(a, b)
def fraction_gcd(x, y):
a = x.numerator
b = x.denominator
c = y.numerator
d = y.denominator
return Fraction(gcd(a, c), lcm(b, d))
print(fraction_gcd(Fraction(2, 3), Fraction(2, 3)))
# 2/3