[Python-Dev] Mixing float and Decimal -- thread reboot (original) (raw)

Guido van Rossum guido at python.org
Wed Mar 24 23:23:11 CET 2010

On Wed, Mar 24, 2010 at 2:29 PM, Raymond Hettinger <raymond.hettinger at 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 "", line 1, in TypeError: unorderable types: complex() < int()_ _z < float()_ _Traceback (most recent call last):_  _File "", line 1, in TypeError: unorderable types: complex() < float()_ _z < complex()_ _Traceback (most recent call last):_  _File "", line 1, in 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 "", line 1, in 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)

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