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Operator Precedence/Boolean Logic

Marko Rauhamaa marko at pacujo.net
Thu Jun 23 05:53:08 EDT 2016 
Antoon Pardon <antoon.pardon at rece.vub.ac.be>:

> Op 23-06-16 om 11:10 schreef Marko Rauhamaa:
>> The __len__ method is not guaranteed to execute in O(1). See:
>>
>>    <URL: https://docs.python.org/3/reference/datamodel.html?highlig
>>    ht=__len__#object.__len__>
>
> As far as I can see, neither is the __bool__ method.

Correct, but in the absence of an __empty__ method, __bool__ gives the
class the best opportunity to check for emptiness quickly.

This is not only a theoretical concern. It's quite common for data
structures not to maintain an element count because it's extra baggage
that's not always needed and any application could keep a track of.
However, an emptiness check is often trivial.


Marko
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