Is it reasonable to declare an exception type for a single function?

Question

Say I have this code:

def wait_for_x(timeout_at=None):
    while condition_that_could_raise_exceptions
        if timeout_at is not None and time.time() > timeout_at:
            raise SOMEEXCEPTIONHERE

        do_some_stuff()

try:
    foo()
    wait_for_x(timeout_at=time.time() + 10)
    bar()
except SOMEEXCEPTIONHERE:
    # report timeout, move on to something else

How do I pick an exception type SOMEEXCEPTIONHERE for the function? Is it reasonable to create a unique exception type for that function, so that there's no danger of condition_that_could_raise_exceptions raising the same exception type?

wait_for_x.Timeout = type('Timeout', (Exception,), {})

Answer 1

If distinguishing exceptions from wait_for_x from those from condition_that_could_raise_exceptions is important enough, then sure, define a new exception type. After all, the type is the main way of distinguishing different kinds of exceptions, and parsing the message tends to get messy pretty quickly.