[Numpy-discussion] boolean arrays

Gael Varoquaux gael.varoquaux at normalesup.org
Thu Nov 26 08:44:07 EST 2009

On Thu, Nov 26, 2009 at 02:43:14PM +0100, Fabrice Silva wrote:
> Le jeudi 26 novembre 2009 à 18:26 +0200, Nadav Horesh a écrit :
> > It is obvious to me that True+False == True,. Why do you think it should
> > be False?

> I would understand it is not obvious that '+' stands for logical 'or',
> and '*' for logical 'and'...

In Bool's algebra, this is the common convention. The reason being that
only 'or' can correspond to the additive law of an algebra: its null
element is absorbant for 'and'.

In other words, if you map '+' and '*' to the opposite, you'll get
suprising behaviors.


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