[Python-3000] Use cases for type annotations?

[Marcin 'Qrczak' Kowalczyk]

"Steven Bethard" <steven.bethard at gmail.com> writes:

> (1) there were very few real implementations of the ideas, and
> (2) where there was an implementation, it relied on concrete types

Common Lisp has:

- Classes ("concrete types"), with explicit subclassing,
  not parametrized, defined strictly, used for dispatch.

- Types, with various ad-hoc notations for builtin concepts (like
  integer ranges, arrays with specialized element types, functions
  with specific argument and result types), where asking for subtyping
  has three possible outcomes ("yes", "no", "I don't know", with
  partially implementation-dependent distribution), used mainly for
  optimization based on explicit declarations, and sometimes for
  expressing predicates to be tested against concrete objects.

Python seems to want to archieve both goals with one system.
I'm sceptic.

-- 
   __("<         Marcin Kowalczyk
   \__/       qrczak at knm.org.pl
    ^^     http://qrnik.knm.org.pl/~qrczak/