[issue7279] decimal.py: == and != comparisons involving NaNs
report at bugs.python.org
Tue Mar 23 15:57:47 CET 2010
Mark Dickinson <dickinsm at gmail.com> added the comment:
Re-opening to address a couple of points that came out of the python-dev discussion:
(1) As Stefan pointed out on python-dev, equality and inequality comparisons involving signaling nans should signal (order comparisons already do). IEEE 754 is fairly clear on this. From section 6.2:
"""Signaling NaNs shall be reserved operands that, under default exception handling, signal the invalid operation exception (see 7.2) for every general-computational and signaling-computational operation except for the conversions described in 5.12."""
(Comparisons fall under 'signaling-computational operations, in section 5.6 of the standard.)
I propose to fix this for 2.7 and 3.2.
(2) Currently hash(Decimal("nan")) raises a TypeError. I can see no good reason for this at all; it's possible to hash float nans and to put them in sets and dictionaries. I propose to remove this restriction for 2.7 and 3.2. I think hash(Decimal("snan")) should also succeed: *computational* operations on signaling nans should signal, but I don't think that putting a signaling nan into a dict, or checking for its presence in a list, counts as a computational operation for this purpose.
assignee: -> mark.dickinson
priority: -> high
status: closed -> open
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