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Operator Precedence/Boolean Logic

Elizabeth Weiss cake240 at gmail.com
Thu Jun 23 00:22:09 EDT 2016 
On Wednesday, June 22, 2016 at 3:42:24 AM UTC-4, Lawrence D’Oliveiro wrote:
> On Wednesday, June 22, 2016 at 3:40:22 PM UTC+12, Elizabeth Weiss wrote:
> > I am a little confused as to how this is False:
> > 
> > False==(False or True)
> > 
> > I would think it is True because False==False is true. 
> > 
> > I think the parenthesis are confusing me. 
> 
> No, it is the meanings of the boolean operators in Python. The rules are:
> 
> * boolean operators don’t have to operate on boolean values. The language spec <https://docs.python.org/3/reference/expressions.html#boolean-operations> says:
> 
>     “...the following values are interpreted as false: False, None, numeric
>     zero of all types, and empty strings and containers (including strings,
>     tuples, lists, dictionaries, sets and frozensets). All other values are
>     interpreted as true.”
> 
> I feel that’s a needlessly complicated rule. It would have been simpler if boolean operators (and conditional expressions like in if-statements and while-statements) only allowed values of boolean types. But that’s one of the few warts in the design of Python...
> 
> * the meaning of “A or B” is: “return A if it evaluates to true, else return B”. Correspondingly, the meaning of “A and B” is: “return A if it evaluates to false, else return B”.
> 
> Does that give you enough clues to understand what is going on?

Thanks, Lawrence!
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