NameError after Dill/Marshal deserialisation

Question

I am trying to dump a compiled piece of compiled Python code using either marshal or dill.

The source is compiled with compiled(src, "<source>", "exec", optimize=2), the compiled code does run well.

However, when the compiled code is dumped with either dill or marshal, and loaded again, the code raises NameError as in the example below.

Code example:

1. File source.py

   import sympy
   pp = sympy.pprint
   x = sympy.Symbol("x")
   def p(*args):
      try:
         pp(*args)
      except TypeError:
         print(*args)
   p(5*x+1)
   

2. File compiler.py

   import dill
   #import marshal
   
   with open("source.py") as fp:
      src = fp.read()
   compiled = compile(src, "<source>", "exec", optimize=2)
   exec(compiled)             # ok
   obj = dill.dumps(compiled)
   loaded = dill.loads(obj)
   exec(loaded)               # NameError: name "pp" is not defined
   

How can I fix this? And if it is intended behaviour, is there any alternatives to serialise/deserialise the compiled code? (I am not concerned about security yet.)