def user_func():
    Mouse.eat(Cheese)
    if Cat.find(Mouse):
        Cat.happy += 1

def framework_wrap(user_func):
    # this is a framework internal and has name bindings to Cat, Mouse and Cheese
    def f():
        inject(user_func, {'Cat': Cat, 'Mouse': Mouse, 'Cheese': Cheese})
        user_func()
    return f

@framework_wrap
def user_func():

nonlocal Cat, Mouse, Cheese

import types
import opcode

# Opcode constants used for comparison and replacecment
LOAD_FAST = opcode.opmap['LOAD_FAST']
LOAD_GLOBAL = opcode.opmap['LOAD_GLOBAL']
STORE_FAST = opcode.opmap['STORE_FAST']

DEBUGGING = True

def append_arguments(code_obj, new_locals):
    co_varnames = code_obj.co_varnames   # Old locals
    co_names = code_obj.co_names      # Old globals
    co_argcount = code_obj.co_argcount     # Argument count
    co_code = code_obj.co_code         # The actual bytecode as a string

    # Make one pass over the bytecode to identify names that should be
    # left in code_obj.co_names.
    not_removed = set(opcode.hasname) - set([LOAD_GLOBAL])
    saved_names = set()
    for inst in instructions(co_code):
        if inst[0] in not_removed:
            saved_names.add(co_names[inst[1]])

    # Build co_names for the new code object. This should consist of
    # globals that were only accessed via LOAD_GLOBAL
    names = tuple(name for name in co_names
                  if name not in set(new_locals) - saved_names)

    # Build a dictionary that maps the indices of the entries in co_names
    # to their entry in the new co_names
    name_translations = dict((co_names.index(name), i)
                             for i, name in enumerate(names))

    # Build co_varnames for the new code object. This should consist of
    # the entirety of co_varnames with new_locals spliced in after the
    # arguments
    new_locals_len = len(new_locals)
    varnames = (co_varnames[:co_argcount] + new_locals +
                co_varnames[co_argcount:])

    # Build the dictionary that maps indices of entries in the old co_varnames
    # to their indices in the new co_varnames
    range1, range2 = xrange(co_argcount), xrange(co_argcount, len(co_varnames))
    varname_translations = dict((i, i) for i in range1)
    varname_translations.update((i, i + new_locals_len) for i in range2)

    # Build the dictionary that maps indices of deleted entries of co_names
    # to their indices in the new co_varnames
    names_to_varnames = dict((co_names.index(name), varnames.index(name))
                             for name in new_locals)

    if DEBUGGING:
        print"injecting: {0}".format(new_locals)
        print"names: {0} -> {1}".format(co_names, names)
        print"varnames: {0} -> {1}".format(co_varnames, varnames)
        print"names_to_varnames: {0}".format(names_to_varnames)
        print"varname_translations: {0}".format(varname_translations)
        print"name_translations: {0}".format(name_translations)


    # Now we modify the actual bytecode
    modified = []
    for inst in instructions(code_obj.co_code):
        # If the instruction is a LOAD_GLOBAL, we have to check to see if
        # it's one of the globals that we are replacing. Either way,
        # update its arg using the appropriate dict.
        if inst[0] == LOAD_GLOBAL:
            print"LOAD_GLOBAL: {0}".format(inst[1])
            if inst[1] in names_to_varnames:
                print"replacing with {0}:".format(names_to_varnames[inst[1]])
                inst[0] = LOAD_FAST
                inst[1] = names_to_varnames[inst[1]]
            elif inst[1] in name_translations:    
                inst[1] = name_translations[inst[1]]
            else:
                raise ValueError("a name was lost in translation")
        # If it accesses co_varnames or co_names then update its argument.
        elif inst[0] in opcode.haslocal:
            inst[1] = varname_translations[inst[1]]
        elif inst[0] in opcode.hasname:
            inst[1] = name_translations[inst[1]]
        modified.extend(write_instruction(inst))

    code = ''.join(modified)
    # Done modifying codestring - make the code object

    return types.CodeType(co_argcount + new_locals_len,
                          code_obj.co_nlocals + new_locals_len,
                          code_obj.co_stacksize,
                          code_obj.co_flags,
                          code,
                          code_obj.co_consts,
                          names,
                          varnames,
                          code_obj.co_filename,
                          code_obj.co_name,
                          code_obj.co_firstlineno,
                          code_obj.co_lnotab)


def instructions(code):
    code = map(ord, code)
    i, L = 0, len(code)
    extended_arg = 0
    while i < L:
        op = code[i]
        i+= 1
        if op < opcode.HAVE_ARGUMENT:
            yield [op, None]
            continue
        oparg = code[i] + (code[i+1] << 8) + extended_arg
        extended_arg = 0
        i += 2
        if op == opcode.EXTENDED_ARG:
            extended_arg = oparg << 16
            continue
        yield [op, oparg]

def write_instruction(inst):
    op, oparg = inst
    if oparg is None:
        return [chr(op)]
    elif oparg <= 65536L:
        return [chr(op), chr(oparg & 255), chr((oparg >> 8) & 255)]
    elif oparg <= 4294967296L:
        return [chr(opcode.EXTENDED_ARG),
                chr((oparg >> 16) & 255),
                chr((oparg >> 24) & 255),
                chr(op),
                chr(oparg & 255),
                chr((oparg >> 8) & 255)]
    else:
        raise ValueError("Invalid oparg: {0} is too large".format(oparg))



if __name__=='__main__':
    import dis

    class Foo(object):
        y = 1

    z = 1
    def test(x):
        foo = Foo()
        foo.y = 1
        foo = x + y + z + foo.y
        print foo

    code_obj = append_arguments(test.func_code, ('y',))
    f = types.FunctionType(code_obj, test.func_globals, argdefs=(1,))
    if DEBUGGING:
        dis.dis(test)
        print '-'*20
        dis.dis(f)
    f(1)

# framework objects
class Cat: pass
class Mouse: pass
class Cheese: pass

_namespace = {'Cat':Cat, 'Mouse':Mouse, 'Cheese':Cheese } # names to be injected

# framework decorator
from functools import wraps
def wrap(f):
    func_globals = f.func_globals if hasattr(f,'func_globals') else f.__globals__
    @wraps(f)
    def wrapped(*args, **kwargs):
        # determine which names in framework's _namespace collide and don't
        preexistent = set(name for name in _namespace if name in func_globals)
        nonexistent = set(name for name in _namespace if name not in preexistent)
        # save any preexistent name's values
        f.globals_save = {name: func_globals[name] for name in preexistent}
        # temporarily inject framework's _namespace
        func_globals.update(_namespace)

        retval = f(*args, **kwargs) # call function and save return value

        # clean up function's namespace
        for name in nonexistent:
             del func_globals[name] # remove those that didn't exist
        # restore the values of any names that collided
        func_globals.update(f.globals_save)
        return retval

    return wrapped

from __future__ import print_function
import framework

class Cat: pass  # name that collides with framework object

@framework.wrap
def user_func():
    print('in user_func():')
    print('  Cat:', Cat)
    print('  Mouse:', Mouse)
    print('  Cheese:', Cheese)

user_func()

print()
print('after user_func():')
for name in framework._namespace:
    if name in globals():
        print('  {} restored to {}'.format(name, globals()[name]))
    else:
        print('  {} not restored, does not exist'.format(name))

in user_func():
  Cat: <class 'framework.Cat'>
  Mouse: <class 'framework.Mouse'>
  Cheese: <class 'framework.Cheese'>

after user_func():
  Cheese not restored, does not exist
  Mouse not restored, does not exist
  Cat restored to <class '__main__.Cat'>

from animal_farm import Goat
cheese = make_cheese(Goat().milk())