On Wed, Mar 24, 2010 at 2:29 PM, Raymond Hettinger <raymond.hettin...@gmail.com> wrote: > > On Mar 24, 2010, at 2:09 PM, Mark Dickinson wrote: > >> Slight change of topic. I've been implementing the extra comparisons >> required for the Decimal type and found an anomaly while testing. >> Currently in py3k, order comparisons (but not ==, !=) between a >> complex number and another complex, float or int raise TypeError: >> >>>>> z = complex(0, 0) >>>>> z < int() >> Traceback (most recent call last): >> File "<stdin>", line 1, in <module> >> TypeError: unorderable types: complex() < int() >>>>> z < float() >> Traceback (most recent call last): >> File "<stdin>", line 1, in <module> >> TypeError: unorderable types: complex() < float() >>>>> z < complex() >> Traceback (most recent call last): >> File "<stdin>", line 1, in <module> >> TypeError: unorderable types: complex() < complex() >> >> But Fraction is the odd man out: a comparison between a Fraction and >> a complex raises a TypeError for complex numbers with nonzero >> imaginary component, but returns a boolean value if the complex number >> has zero imaginary component: >> >>>>> z < Fraction() >> False >>>>> complex(0, 1) < Fraction() >> Traceback (most recent call last): >> File "<stdin>", line 1, in <module> >> TypeError: unorderable types: complex() < Fraction() >> >> I'm tempted to call this Fraction behaviour a bug, but maybe it arises >> from the numeric integration themes of PEP 3141. Any ideas? > > Conceptually, it's a bug. The numeric tower treats non-complex > numbers as special cases of complex where the imaginary > component is zero (that's why the non-complex types all support > real/imag), and since complex numbers are not allowed to compare > to themselves, they shouldn't compare to anything else either.
That's how I read the PEP too. PEP 3141 doesn't define any ordering operations on Complex, they only show up on Real. > To confirm, we should ask Jeffrey Y to opine. CC'ed him. After all looks like it was he who added it to Fraction. :-) -- --Guido van Rossum (python.org/~guido) _______________________________________________ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
