Akira Li added the comment: Whether or not gcd(a, b) == gcd(|a|, |b|) depends on the definition if we believe to Stepanov of C++ STL fame who mentions in his lecture [1]
[1] http://www.stepanovpapers.com/gcd.pdf that the current implementation that uses two operation __bool__ and __mod__: def gcd(a, b): while b: a, b = b, a%b return a can be applied to Euclidean ring elements (not just positive or negative integers). Despite Knuthâs objection to gcd(1, -1) = -1, adding `if a < 0: a = -a` at the end changes the requirements for the type. Here's the definition from the lecture [1]: Greatest common divisor is a common divisor that is divisible by any other common divisor. I have no opinion on whether or not fractions.gcd() should be changed. I thought that I should mention that different definitions exist. ---------- nosy: +akira _______________________________________ Python tracker <rep...@bugs.python.org> <http://bugs.python.org/issue22477> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
