Expression can be simplified on list

[Rustom Mody]

On Thursday, September 15, 2016 at 1:43:05 AM UTC+5:30, Terry Reedy wrote:
> On 9/14/2016 3:16 AM, Rustom Mody wrote:
> 
> > In THOSE TYPES that element can justifiably serve as a falsey (empty) type
> >
> > However to extrapolate from here and believe that ALL TYPES can have a falsey
> > value meaningfully, especially in some obvious fashion, is mathematically nonsense.
> 
> Python make no such nonsense claim.  By default, Python objects are truthy.
> 
>  >>> bool(object())
> True
> 
> Because True is the default, object need not and at least in CPython 
> does not have a __bool__ (or __len__) method.  Classes with no falsey 
> objects, such as functions, generators, and codes, need not do anything 
> either.  In the absence of an override function, the internal bool code 
> returns True.
> 
Not sure what you are trying to say Terry...
Your English suggests you disagree with me
Your example is exactly what I am saying; if a type has a behavior in which
all values are always True (true-ish) its a rather strange kind of bool-nature.

Shall we say it has Buddha-nature? ;-)

> It is up to particular classes to override that default and say that it 
> has one or more Falsey objects.  They do so by defining a __bool__ 
> method that returns False for the falsey objects (and True otherwise) or 
> by defining a __len__ method that returns int 0 for falsey objects (and 
> non-0 ints otherwise).  If a class defines both, __bool__ wins.

Sure one can always (ok usually) avoid a bug in a system by not using the 
feature that calls up the bug. Are you suggesting that that makes the bug non-exist?

In more detail:
- If user/programmer defines a new type
- Which has no dunder bool
- Which has no dunder len
- Which has no ... (all the other things like len that can make for a 
non-trivial bool behavior)
- And then uses a value of that type in a non-trivial bool-consuming position
such as the condition of an if/while etc

There's a very good chance that bool-usage is buggy

In more mundane terms, dunder bool defaulting to true is about as useful 
as if it defaulted to
2*random.random()

Why not default it in the way that AttributeError/NameError/TypeError etc
are raised?