Improved nestedmodule decorator implementation

[Gregory Ewing]

I wrote:
> The only shortcoming I can think of is that a nestedmodule
> inside another nestedmodule won't be able to see the names
> in the outer nestedmodule

Actually, that's not correct -- the version I posted before
actually crashes if you try to refer to a name in an outer
nestedmodule from an inner nestedmodule.

Here's an improved version that fully supports nesting to
any depth.

% python3 test_nested_nested.py
foo
blarg

#------------------------------------------
#
#   test_nested_nested.py
#
#------------------------------------------

from nestedmodule import nestedmodule

@nestedmodule
def m1():

     def foo():
         print("foo")

     @nestedmodule
     def m2():

         def blarg():
             foo()
             print("blarg")

m1.m2.blarg()

#------------------------------------------
#
#   nestedmodule.py
#
#------------------------------------------

from types import CodeType, FunctionType, ModuleType
from dis import dis

def hack_code(f):
     """Hack 'return locals()' onto the end of the bytecode of f."""
     code1 = f.__code__
     bytes1 = code1.co_code
     names1 = code1.co_names
     n = len(names1)
     names2 = names1 + ('locals',)
     bytes2 = bytes1[:-4] + bytes([116, n, 0, 131, 0, 0, 83])
     code2 = CodeType(code1.co_argcount, code1.co_kwonlyargcount, code1.co_nlocals,
         code1.co_stacksize, code1.co_flags, bytes2, code1.co_consts, names2,
         code1.co_varnames, code1.co_filename, code1.co_name, code1.co_firstlineno,
         code1.co_lnotab, code1.co_freevars, code1.co_cellvars)
     f2 = FunctionType(code2, f.__globals__, f.__name__, f.__kwdefaults__, 
f.__closure__)
     return f2

def nestedmodule(f):
     f2 = hack_code(f)
     l = f2()
     m = ModuleType(f.__name__)
     m.__dict__.update(l)
     return m