missing 'xor' Boolean operator

Jean-Michel Pichavant jeanmichel at sequans.com
Thu Jul 16 15:53:45 CEST 2009


Emile van Sebille wrote:
> On 7/16/2009 2:06 AM Jean-Michel Pichavant said...
>> Ok then, why "or" does not return True, if the first element is 
>> considered True ? Why returning the element itself. Any reason for 
>> that ? Because it's confusing, maybe people used to that logic find 
>> it obvious, but I really don't.
>
> For example, I sometimes use it to set defaults:
>
> daysInAdvance = int(inputVar) or 25
>
> Emile
>
Sure this looks like an elegant way to set default values and I will use 
this form , but I'm not sure this justifies by itself the trickery. 
Python has extended the algebra definition of "or" and "and" top any 
type, but it is so unintuitive (I'm no LISP programmer). I think than 
using the short-circuiting mechanism of bool operators along with the 
python tricks is just error prone and may result in bug difficult to 
spot, unless you are very aware of all python boolean mechanisms.

JM




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