On Thu, Jan 12, 2012 at 3:03 PM, Terry Reedy <tjre...@udel.edu> wrote: > On 1/12/2012 3:45 PM, Nathan Rice wrote: <snip> >>>>> print isinstance(3, const) >> >> True > > > A Contraints instance defines a set. 'const' is the set 'odd_ge_3' > It would look better if you used standard syntax and do the inclusion check > in a __contains__ method. > >>>> 3 in odd_ge_3 > > True
But what are types but abstract sets of values? Phrasing it as a typecheck is perfectly sensible from a type-theoretic standpoint. Also, the problem of representing `isinstance(X.attr, someclass)` [for non-Constraint someclass, e.g. str] in a Constraint would still remain, since there's no "__lcontains__" (thus precluding `X.attr in str`). <snip> >> so your validations are checked using __instancecheck__. > > But it is a fake check in that 3 is not really an instance of the class, > which has no instances. The same can be true for abstract base classes, which have been sufficiently accepted to warrant adding __instancecheck__() in the first place and also to be added to the std lib (witness the `abc` and `collections` modules). It may seem unfamiliar, but then again it was only made possible starting with v2.6, which is pretty recent. Cheers, Chris -- http://rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
