On 4/29/11 1:35 AM, Nick Coghlan wrote:
On Fri, Apr 29, 2011 at 3:28 PM, Steven D'Aprano<st...@pearwood.info> wrote:
Robert Kern wrote:
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.
Aside from the divide-by-zero case, we treat NaNs as quiet NaNs.
And in fact, 0.0/0.0 is covered by the more general rule that x/0.0 raises
ZeroDivisionError, not a rule that converts IEEE-754 INVALID exceptions into
Python exceptions. Other operations that produce a NaN and issue an IEEE-754
INVALID signal do not raise a Python exception.
But that's not the difference between signalling NaNs and quiet NaNs. A
signalling NaN is one that when it is used as an *input* to an operation, it
issues an INVALID signal, not whether a signal is issued when it is the *output*
of an operation.
--
Robert Kern
"I have come to believe that the whole world is an enigma, a harmless enigma
that is made terrible by our own mad attempt to interpret it as though it had
an underlying truth."
-- Umberto Eco
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