Operator Precedence/Boolean Logic

Lawrence D’Oliveiro lawrencedo99 at gmail.com
Thu Jun 23 00:47:05 EDT 2016

On Thursday, June 23, 2016 at 3:12:52 PM UTC+12, Larry Hudson wrote:
> On 06/22/2016 12:42 AM, Lawrence D’Oliveiro wrote:
>> * 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...
> Wart??  I *strongly* disagree.  I find it one of the strengths of Python,
> it enhances Python's expressiveness.

Tightening it up would rule out a whole class of common errors, from misunderstanding (or forgetting) the rule about what exactly gets interpreted as true and what as false <https://bugs.python.org/issue13936> <http://stackoverflow.com/questions/28116931/datetime-time0-0-evaluates-as-false-in-boolean-context>.

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