import types
import inspect


class Foo:
    def say(self):
        print("Foo.say")

class Bar:
    def say(self):
        print("Bar.say")

if __name__ == '__main__':
    f = Foo()
    b = Bar()

    setattr(b, 'say', types.MethodType(f.say, b))

    # Should get the source of Foo.foo but instead fails.
    source = inspect.getsource(b.say)
    print(source)