Operator Precedence/Boolean Logic

[Rustom Mody]

On Thursday, June 30, 2016 at 10:52:50 PM UTC+5:30, Steven D'Aprano wrote:
> Okay, if you think that automata cannot be empty, I'll accept that. In that
> case, then I'll change my answer and say that __bool__ for automata should
> simply return True. All automata should be truthy.
> 

I am not sure with what tone of voice you are saying that

If ... “return True” is about as good -- ie useful -- as (say)

def __bool__(self):
  from random import random
  return int(2*random())

then I think we agree

But then there is a well-established behavior pattern in python
captured by the contexts that raise AttributeError/NameError/TypeError etc
viz For things that are undefined we are told politely they are undefined

IOW Why say something is useless and define it rather than just leave undefined
something that is ill-defined.

If on the other hand you are giving that “return True”as a serious useful definition?

If both you and Chris tripped up on a right definition of an “empty” automaton
and regex respectively, I believe it demonstrates that getting boolishness
for an arbitrary type right is at least non-trivial. [FWIW My belief: In
general its nonsensical]