[Python-3000] optional argument annotations

[Tony Lownds]

I have a working optional argument syntax implementation, I'm hoping  
to get some direction on
the implementation decisions so far.... please see below.

Python 3.0x (p3yk:52824M, Nov 23 2006, 09:22:23)
[GCC 3.4.4 20050721 (Red Hat 3.4.4-2)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
 >>> def f()-> 1: pass
...
 >>> f.func_returns
1
 >>> def f(): pass
...
 >>> f.func_annotations
 >>> f.func_returns
Traceback (most recent call last):
   File "<stdin>", line 1, in <module>
AttributeError: 'function' object has no attribute 'func_returns'
 >>> def f(x:1): pass
...
 >>> f.func_annotations
{'x': 1}
 >>>
 >>> import dis
 >>> dis.dis(compile("def f(x:1, y:2=3, z=4)->5:pass", "<str>", "exec"))
   1           0 LOAD_CONST               0 (3)         # default for y
               3 LOAD_CONST               1 (4)          # default for z
               6 LOAD_CONST               2 (1)          # annotation  
for x
               9 LOAD_CONST               3 (2)          # annotation  
for y
              12 LOAD_CONST               4 (6)         # bitmask for  
annotations... 0b110
              15 LOAD_CONST               5 (5)         # func_returns
              18 LOAD_CONST               6 (<code object f at  
0xb7f08848, file "<str>", line 1>)
              21 MAKE_FUNCTION        49154      # numdefaults(2) +  
kwdefaults(0) << 8 + has_annotations(1) << 14 + has_returns(1) << 15
              24 STORE_NAME               0 (f)
              27 LOAD_CONST               7 (None)
              30 RETURN_VALUE

Index: Parser/Python.asdl
===================================================================
--- Parser/Python.asdl  (revision 52824)
+++ Parser/Python.asdl  (working copy)
@@ -9,8 +9,8 @@
             -- not really an actual node but useful in Jython's  
typesystem.
             | Suite(stmt* body)
-       stmt = FunctionDef(identifier name, arguments args,
-                           stmt* body, expr* decorators)
+       stmt = FunctionDef(identifier name, typedarguments args,
+                           stmt* body, expr* decorators, expr? returns)
               | ClassDef(identifier name, expr* bases, stmt* body)
               | Return(expr? value)
@@ -102,6 +102,9 @@
         arguments = (expr* args, identifier? vararg, expr* kwonlyargs,
                          identifier? kwarg, expr* defaults, expr*  
kw_defaults)
+       typedarguments = (annotatedarg* args, identifier? vararg,  
expr* kwonlyargs,
+                        identifier? kwarg, expr* defaults, expr*  
kw_defaults)
+       annotatedarg = (expr arg, expr? annotation)
          -- keyword arguments supplied to call
          keyword = (identifier arg, expr value)