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| -rw-r--r-- | Doc/library/math.rst | 19 |
1 files changed, 17 insertions, 2 deletions
diff --git a/Doc/library/math.rst b/Doc/library/math.rst index 145bac4966..d485ae5c27 100644 --- a/Doc/library/math.rst +++ b/Doc/library/math.rst @@ -627,8 +627,23 @@ 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 .. versionadded:: 3.5 |