https://github.com/python/cpython/commit/182e93c3f57b0c72e765c9896066d32e461... commit: 182e93c3f57b0c72e765c9896066d32e461c0865 branch: main author: Charlie Zhao <zhaoyu_hit@qq.com> committer: JelleZijlstra <jelle.zijlstra@gmail.com> date: 2022-04-02T12:58:03-07:00 summary: bpo-47031: Improve documentation for `math.nan` (GH-32170) Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com> files: M Doc/library/math.rst diff --git a/Doc/library/math.rst b/Doc/library/math.rst index bcbcdef51d3fc..c0f9614231912 100644 --- a/Doc/library/math.rst +++ b/Doc/library/math.rst @@ -646,8 +646,23 @@ Constants .. data:: nan - A floating-point "not a number" (NaN) value. Equivalent to the output of - ``float('nan')``. + A floating-point "not a number" (NaN) value. Equivalent to the output of + ``float('nan')``. Due to the requirements of the `IEEE-754 standard + <https://en.wikipedia.org/wiki/IEEE_754>`_, ``math.nan`` and ``float('nan')`` are + not considered to equal to any other numeric value, including themselves. To check + whether a number is a NaN, use the :func:`isnan` function to test + for NaNs instead of ``is`` or ``==``. + Example:: + + >>> import math + >>> math.nan == math.nan + False + >>> float('nan') == float('nan') + False + >>> math.isnan(math.nan) + True + >>> math.isnan(float('nan')) + True .. versionchanged:: 3.11 It is now always available.