def invalid_dict_pickle_keys(self, msg_dict):
no_pickle_keys = list()<EOL>for key, val in msg_dict.items():<EOL><INDENT>try:<EOL><INDENT>pickle.dumps(key)<EOL>pickle.dumps(val)<EOL><DEDENT>except TypeError:<EOL><INDENT>no_pickle_keys.append(key)  <EOL><DEDENT>except pickle.PicklingError:<EOL><INDENT>no_pickle_keys.append(key)  <EOL><DEDENT>except pickle.UnpickleableError:<EOL><INDENT>no_pickle_keys.append(key)  <EOL><DEDENT><DEDENT>return no_pickle_keys<EOL>
Return a list of keys that can't be pickled.  Return [] if 
        there are no pickling problems with the values associated with the
        keys.  Return the list of keys, if there are problems.