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? -- https://mail.python.org/mailman/listinfo/python-list
