Clarify meaning of bare Tuple, etc. (#110)

Fixes python/typing#284

Author: ilevkivskyi

pep-0484.txt

@@ -1019,6 +1019,33 @@ the other hand, when a value has type ``Any``, the type checker will
 allow all operations on it, and a value of type ``Any`` can be assigned
 to a variable (or used as a return value) of a more constrained type.
 
+A function parameter without an annotation is assumed to be annotated with
+``Any``. If a gneric type is used without specifying type parameters,
+they assumed to be ``Any``::
+
+  from typing import Mapping
+
+  def use_map(m: Mapping) -> None:  # Same as Mapping[Any, Any]
+      ...
+
+This rule also applies to ``Tuple``, in annotation context it is equivalent
+to ``Tuple[Any, ...]`` and, in turn, to ``tuple``. As well, a bare
+``Callable`` in an annotation is equivalent to ``Callable[[...], Any]`` and,
+in turn, to ``collections.abc.Callable``::
+
+  from typing import Tuple, List, Callable
+
+  def check_args(args: Tuple) -> bool:
+      ...
+
+  check_args(())           # OK
+  check_args((42, 'abc'))  # Also OK
+  check_args(3.14)         # Flagged as error by a type checker
+
+  # A list of arbitrary callables is accepted by this function
+  def apply_callbacks(cbs: List[Callable]) -> None:
+      ...
+
 
 The type of class objects
 -------------------------