human
I wrote the below code

    def copy(future):
        assert (future is a)
        if (isinstance(a, TracebackFuture) and isinstance(b, TracebackFuture) and (a.exc_info() is not None)):
            b.set_exc_info(a.exc_info())
        elif (a.exception() is not None):
            b.set_exception(a.exception())
        else:
            b.set_result(a.result())
    a.add_done_callback(copy)

What's a good function header?

Here's a good function header?
assistant
#Here's a good function header.

def chain_future(a, b):