a question about python

[李白，字一日]

hi,
i have a question on python programming.

let file a.py has a class named a,
  class a():
    __G__ = "1111"

in file b.py i need to insert an attribute __C__ to class a

it would be as if class a defined in file a.py like this:
  class a():
    __G__ = "1111"
    __C__ = "22222"

how this be done in python without inheritance?