[Python-Dev] Not-a-Number (original) (raw)

Steven D'Aprano steve at pearwood.info
Fri Apr 29 08:49:49 CEST 2011

Ben Finney wrote:

Steven D'Aprano <steve at pearwood.info> writes:

Robert Kern wrote: On 4/28/11 8:44 PM, Steven D'Aprano wrote:

The real question should be, why does Python treat all NANs as signalling NANs instead of quiet NANs? I don't believe this helps anyone. Actually, Python treats all NaNs as quiet NaNs and never signalling NaNs. Sorry, did I get that backwards? I thought it was signalling NANs that cause a signal (in Python terms, an exception)? If I do x = 0.0/0 I get an exception instead of a NAN. Hence a signalling NAN. Robert has interpreted your “treats all NaNs as signalling NaNs” to mean “treats all objects that Python calls a NaN as signalling NaNs”, and is pointing out that no, the objects that Python calls “NaN” are all quiet NaNs.

I'm sorry for my lack of clarity. I'm referring to functions which potentially produce NANs, not the exceptions themselves. A calculation which might have produced a (quiet) NAN as the result instead raises an exception (which I'm treating as equivalent to a signal).

-- Steven

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