[issue6675] inf == inf (wrong IEEE 754 behaviour)

[D Hardy]

New submission from D Hardy <diggory.hardy at gmail.com>:

Currently python evaluates infinity as equal to itself in my tests (2.6.2 and 3.0.1+
from ubuntu). I'm not entirely sure whether the behaviour of 'inf == inf' is specified
by IEEE 754, but it leads to results like:

>>> 1e400
inf
>>> 1e400 == 1e500
True

And hence unittests which use tests like

if not (math.fabs(value1 - value2) <= 0.00000001 *
max(math.fabs(value1),math.fabs(value2))):
    fail

don't always fail when they should (when a value is inf).

This is a specific example (and probably not the recommended way of testing
values in any case), but I think "inf != inf" is generally considered the correct
behaviour. (Although maybe this is left over from the PEP 42 / PEP 754 mess; I
wasn't able to find the current status of implementing IEEE 754 behaviour in
python.)

----------
components: None
messages: 91443
nosy: Cyborg16
severity: normal
status: open
title: inf == inf (wrong IEEE 754 behaviour)
type: behavior
versions: Python 2.6, Python 3.0

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue6675>
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