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| author |   Tony Flury <anthony.flury@btinternet.com> | 2018-09-14 18:48:50 +0100 |
|---|---|---|
| committer |   Benjamin Peterson <benjamin@python.org> | 2018-09-14 10:48:50 -0700 |
| commit | ad8a0004206ba7aec5a8a60fce413da718080db2 (patch) | |
| tree | e2b36f7816a1a1bc5d7d3ee255d7ace410f68401 /Doc/reference/expressions.rst | |
| parent | bpo-34672: Don't pass NULL to gmtime_r. (GH-9312) (diff) | |
| download | cpython-ad8a0004206ba7aec5a8a60fce413da718080db2.tar.gz cpython-ad8a0004206ba7aec5a8a60fce413da718080db2.tar.bz2 cpython-ad8a0004206ba7aec5a8a60fce413da718080db2.zip | |
closes bpo-28955: Clarified comparisons between NaN and number in reference documentation (GH-5982)
Co-authored-by: Benjamin Peterson <benjamin@python.org>
Diffstat (limited to 'Doc/reference/expressions.rst')
| -rw-r--r-- | Doc/reference/expressions.rst | 11 |
1 files changed, 5 insertions, 6 deletions
diff --git a/Doc/reference/expressions.rst b/Doc/reference/expressions.rst index 33f7575a8fc..f4b16182829 100644 --- a/Doc/reference/expressions.rst +++ b/Doc/reference/expressions.rst @@ -1336,12 +1336,11 @@ built-in types. involved, they compare mathematically (algorithmically) correct without loss of precision. - The not-a-number values :const:`float('NaN')` and :const:`Decimal('NaN')` - are special. They are identical to themselves (``x is x`` is true) but - are not equal to themselves (``x == x`` is false). Additionally, - comparing any number to a not-a-number value - will return ``False``. For example, both ``3 < float('NaN')`` and - ``float('NaN') < 3`` will return ``False``. + The not-a-number values ``float('NaN')`` and ``decimal.Decimal('NaN')`` are + special. Any ordered comparison of a number to a not-a-number value is false. + A counter-intuitive implication is that not-a-number values are not equal to + themselves. For example, if ``x = float('NaN')``, ``3 < x``, ``x < 3``, ``x + == x``, ``x != x`` are all false. This behavior is compliant with IEEE 754. * Binary sequences (instances of :class:`bytes` or :class:`bytearray`) can be compared within and across their types. They compare lexicographically using |