I played around with this, and I think it's basically implementable:

py> import new
py> class with_consts(object):
...     def __init__(self, **consts):
...         self.consts = consts
...     def __call__(self, func):
...         return new.function(func.func_code,
...                             dict(globals(), **self.consts))
...
py> @with_consts(y=123)
... def f(x):
...     return x*y, str
...
py> f(2)
(246, <type 'str'>)

I just update the function globals with the keywords passed to the
decorator.  The only problem is that updates to globals() aren't
reflected in the function's globals:

py> str = 5
py> f(2)
(246, <type 'str'>)

Cheers,
Nick.

 >>> from makeconstpre import make_constants as pre
 >>> import time
 >>> @pre(verbose=True, deftime=time.ctime(), a=1, b=2, c=3, pi=__import__('math').pi)
 ... def foo():
 ...     deftime = __frompresets__
 ...     b, a = __frompresets__
 ...     c = __frompresets__
 ...     pi = __frompresets__
 ...     return locals()
 ...
 __frompresets__ : deftime --> Sat Jan 22 20:18:09 2005
 __frompresets__ : ('b', 'a') --> (2, 1)
 __frompresets__ : c --> 3
 __frompresets__ : pi --> 3.14159265359
 locals --> <built-in function locals>
 >>> import dis
 >>> dis.dis(foo)
   3           0 LOAD_CONST               1 ('Sat Jan 22 20:18:09 2005')
               3 STORE_FAST               3 (deftime)

   4           6 LOAD_CONST               2 ((2, 1))
               9 UNPACK_SEQUENCE          2
              12 STORE_FAST               2 (b)
              15 STORE_FAST               0 (a)

   5          18 LOAD_CONST               3 (3)
              21 STORE_FAST               1 (c)

   6          24 LOAD_CONST               4 (3.1415926535897931)
              27 STORE_FAST               4 (pi)

   7          30 LOAD_CONST               5 (<built-in function locals>)
              33 CALL_FUNCTION            0
              36 RETURN_VALUE
 >>> foo()
 {'a': 1, 'c': 3, 'pi': 3.1415926535897931, 'b': 2, 'deftime': 'Sat Jan 22 20:18:09 2005'}

Not vary tested as yet, but seems to work. I want to eliminate redundant constants if the
same name is assigned = __frompresets__ more than once. Right now I brute force generate
another constant.

[Nick Coghlan]

BTW, unlike default arguments, varname = __frompresets__ will work anywhere in the code,
(for the current decorator version) and the generated byte code will have a load of
an appropriate constant (the same one if the same name is being assigned). This would
be tricky to get right if done in a hidden just-in-time manner only in branches that
used the values, but hidden initialization of the whole presets set at the beginning
should be relatively easy if there are no relocation problems.
So, e.g., for

 >>> presets = dict(a=1, b=2, deftime=__import__('time').ctime())

in the decorator args, the next version will act as if the decorated
function had the source code

 >>> print '%s = __frompresets__' % ', '.join(sorted(presets))
 a, b, deftime = __frompresets__

for the current version, except that it will be hidden.

 >>> from presets import presets, curry
 >>> @presets(verbose=True, a=1, b=2, deftime=__import__('time').ctime())
 ... def foo():
 ...    print (a, b)
 ...    print deftime
 ...

 presets: -- "name(?)" means name may be unused
            a = 1
            b = 2
      deftime = 'Mon Jan 24 12:16:07 2005'

 >>> foo()
 (1, 2)
 Mon Jan 24 12:16:07 2005
 >>> @curry(verbose=True, y=444)
 ... def bar(x=3, y=4):
 ...     return x*y
 ...

 presets: -- "name(?)" means name may be unused
            y = 444

 >>> bar(2)
 888
 >>> bar(2, 3)
 Traceback (most recent call last):
   File "<stdin>", line 1, in ?
 TypeError: bar() takes at most 1 argument (2 given)
 >>> bar()
 1332
 >>> import dis
 >>> dis.dis(bar)
   1           0 LOAD_CONST               1 (444)
               3 STORE_FAST               1 (y)

   3           6 LOAD_FAST                0 (x)
               9 LOAD_FAST                1 (y)
              12 BINARY_MULTIPLY
              13 RETURN_VALUE
 >>> dis.dis(foo)
   1           0 LOAD_CONST               1 ((1, 2, 'Mon Jan 24 12:16:07 2005'))
               3 UNPACK_SEQUENCE          3
               6 STORE_FAST               0 (a)
               9 STORE_FAST               1 (b)
              12 STORE_FAST               2 (deftime)

   3          15 LOAD_FAST                0 (a)
              18 LOAD_FAST                1 (b)
              21 BUILD_TUPLE              2
              24 PRINT_ITEM
              25 PRINT_NEWLINE

   4          26 LOAD_FAST                2 (deftime)
              29 PRINT_ITEM
              30 PRINT_NEWLINE
              31 LOAD_CONST               0 (None)
              34 RETURN_VALUE

Now I have to see whether I can optimize the result with Raymond's make_constants
as two decorators in a row... (pre without keyword args is an alias for Raymond's make_constants,
just handy for the moment)

 >>> from pre import pre
 >>> @pre(verbose=True)
 ... @presets(verbose=True, a=1, b=2, deftime=__import__('time').ctime())
 ... def foo():
 ...    print (a, b)
 ...    print deftime
 ...    print __name__
 ...

 presets: -- "name(?)" means name may be unused
            a = 1
            b = 2
      deftime = 'Mon Jan 24 12:29:21 2005'

 __name__ --> __main__
 >>> foo()
 (1, 2)
 Mon Jan 24 12:29:21 2005
 __main__
 >>> dis.dis(foo)
   1           0 LOAD_CONST               1 ((1, 2, 'Mon Jan 24 12:29:21 2005'))
               3 UNPACK_SEQUENCE          3
               6 STORE_FAST               0 (a)
               9 STORE_FAST               1 (b)
              12 STORE_FAST               2 (deftime)

   3          15 LOAD_FAST                0 (a)
              18 LOAD_FAST                1 (b)
              21 BUILD_TUPLE              2
              24 PRINT_ITEM
              25 PRINT_NEWLINE

   4          26 LOAD_FAST                2 (deftime)
              29 PRINT_ITEM
              30 PRINT_NEWLINE

   5          31 LOAD_CONST               2 ('__main__')
              34 PRINT_ITEM
              35 PRINT_NEWLINE
              36 LOAD_CONST               0 (None)
              39 RETURN_VALUE

    @addprop(verbose=True, x=property(getx, setx, delx))
    def foo():
        x = 123
        return x

etc. Maybe could be used to monitor access to specific locals for debug,
or other uses. Haven't even begun to think about that.

Another thing is to turn selected local defs into constants, since executing
the aggregation-of-parts code that accomplished the def may well be unchanging.
This would reduce the execution cost of nested functions. I guess that is
a specific case of a more general sticky-evaluate-rhs-once kind of directive
for locals that are only assigned in one place. special sentinels could
be used in the decorator keyword values to indicate this treatment of the
associated name, e.g.
    from presets import presets
    @presets(x=presets.STICKY, y=123)
    def foo(y):
        x = initx() # done once on the first call, making x references constant after that
        return x*y

Another thing that could be done is to inject pre and post things like atexit stuff.
Also maybe some adaptation things that is just a buzzword so far that I haven't explored.

BTW, is there another op that needs relocation besides JUMP_ABSOLUTE?

I was wondering about doing code mods by messing with an ast, but a decorator would
have to chase down the source and reparse I guess, in order to do that. It would be
interesting to be able to hook into ast stuff with some kind of metacompile hook (hand waving ;-)

Bye for a while.