[PEP 646] Explicitly allow *args: *Tuple[*Ts, T]

pep-0646.rst

@@ -422,8 +422,8 @@ must be of the type annotated. That is, if we specify ``*args`` to be type ``int
 then *all* arguments must be of type ``int``. This limits our ability to specify
 the type signatures of functions that take heterogeneous argument types.
 
-If ``*args`` is annotated as a type variable tuple, however, the types of the
-individual arguments become the types in the type variable tuple:
+If ``*args`` is annotated as a star-prefixed type variable tuple, however, the
+types of the individual arguments become the types in the type variable tuple:
 
 ::
 
@@ -436,6 +436,19 @@ individual arguments become the types in the type variable tuple:
 If no arguments are passed, the type variable tuple behaves like an
 empty tuple, ``Tuple[()]``.
 
+It is also possible to annotate ``*args`` as a star-prefixed tuple parameterised
+using a type variable tuple. This enables referral to prefixes or suffixes of
+the variadic argument list. For example:
+
+::
+
+    # os.execle takes arguments 'path, arg0, arg1, ..., env'
+    def execle(path: str, *args: *Tuple[*Ts, Mapping[str, str]]) → None: ...
+
+    # Note that this is different to
+    def execle(path: str, *args: *Ts, env: Mapping[str, str]) → None: ...
+    # which would make `env` a keyword-only argument.
+
 Note that, in keeping with the rule that type variable tuples must always
 be used unpacked, annotating ``*args`` as being a plain type variable tuple
 instance is *not* allowed: