[Python-ideas] Why no sign function?

[Nick Coghlan]

Mark Dickinson wrote:
> On Mon, Apr 26, 2010 at 10:36 PM, Mark Dickinson <dickinsm at gmail.com> wrote:
>> If a sign function were implemented, I'd probably want something like
>> IEEE 754's signbit function
> 
> Correction:  it's C99 that has a signbit function.  IEEE 754-2008
> specifies an 'isSignMinus' function with exactly the same semantics:
> values with the sign bit set (including -0.0, -inf, and NaNs whose
> sign bit is set) return True;  other values return False.
> 
> I wouldn't object to a `math.is_signed` function or a
> `float.is_signed` method with these semantics.  It's not clear where
> is the better place:  we have `math.isnan` and `math.isinf`, but
> `float.is_integer`.

"is_signed" would probably be a bad name for this purpose. In typical
compsci parlance, all of our numeric types are signed.

For the semantics you're talking about, math.signbit would be a more
reasonable name. (since we can legitimately answer the question for both
integers and floats, whereas "is_integer" is a pretty redundant question
if you are dealing with an integer type)

Cheers,
Nick.

-- 
Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia
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