On Fri, Sep 30, 2016 at 5:58 AM, Random832 <random...@fastmail.com> wrote: > On Thu, Sep 29, 2016, at 02:47, Rustom Mody wrote: >> 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. > > For a given type T, if all objects of type T are true (true-ish, truthy, > whatever), it does make using an expression of type T in an if-statement > an incoherent thing to do, but it makes using an expression of type > Union[T, NoneType] reasonable.
Or, as it would more commonly be spelled, Optional[T]. Very common situation; re.match was mentioned, and lots of data types can be clearly demonstrated by implementing them in Python using some kind of "optional node" structure - eg a linked list, where the last one has "self.next = None", or a binary tree where leaf nodes have None for both children, or a hash table where empty buckets have None. ChrisA -- https://mail.python.org/mailman/listinfo/python-list
