I have a text input with a handler attached to the keyup event. The problem was that the Selenium send_keys method does not send a keyup event when it completes. There is no special Key for that. For example Key.Up does not solve the problem.
Action Chains has key_up and key_down methods. The problem is they are designed to be used with modifier keys, such as Control. It turns out you can get a keyup event by a key_down immediately followed by a key_up, like this: