[New-bugs-announce] [issue47031] math.nan should note that NANs do not compare equal to anything

[Steven D'Aprano]

New submission from Steven D'Aprano <steve+python at pearwood.info>:

The IEEE-754 requirement that NANs are never equal to anything, even to themselves, is a common stumbling block for those new to the consequences of IEEE-754. See for example #47020.

The documentation for math.nan would be a good place to add a note like

"Due to the requirements of the `IEEE-754 standard <https://en.wikipedia.org/wiki/IEEE_754>`_, math.nan and float('nan') are never equal to any other value, including themselves. Use math.isnan to test for NANs."

https://docs.python.org/3.8/library/math.html#math.nan

----------
assignee: docs at python
components: Documentation
keywords: easy
messages: 415302
nosy: docs at python, steven.daprano
priority: normal
severity: normal
status: open
title: math.nan should note that NANs do not compare equal to anything
type: enhancement
versions: Python 3.10, Python 3.11, Python 3.7, Python 3.8, Python 3.9

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue47031>
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