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From: Chris Angelico <rosuav@gmail.com>
Newsgroups: comp.lang.python
Subject: Re: Operator Precedence/Boolean Logic
Date: Sat, 16 Jul 2016 20:46:14 +1000
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On Sat, Jul 16, 2016 at 8:16 PM, Steven D'Aprano <steve@pearwood.info> wrot=
e:
>> If both you and Chris tripped up on a right definition of an =E2=80=9Cem=
pty=E2=80=9D
>> automaton and regex respectively, I believe it demonstrates that getting
>> boolishness for an arbitrary type right is at least non-trivial. [FWIW M=
y
>> belief: In general its nonsensical]
>
> Firstly, I disagree that I tripped up on anything. You haven't given any
> reason to think that Automata objects shouldn't be truthy, and even if yo=
u
> do, isn't that just a matter of opinion?

I also disagree that I "tripped up", but there is room for differing
decisions in API design, and this is one of them. I can't say
perfectly, from my armchair (which I'm not in anyway - way too
cumbersome for a desktop computer), which objects are capable of being
"empty" and which are not. The implementer of the automaton class or
the regex class has to decide what counts as "empty". As Steven says,
the default is that they're all truthy, and onus is on the implementer
to demonstrate that this object is functionally equivalent to 0 or an
empty collection. (And it's possible for ANYONE to get that wrong - cf
timedelta.)

ChrisA