wx (and wxPython) has two events I miss in PyQt: 

EVT_IDLE that's being sent to a frame. It can be used to update the various widgets according to the application's state
EVT_UPDATE_UI that's being sent to a widget when it has to be repainted and updated, so I can compute its state in the handler

Now, PyQt doesn't seem to have these, and the PyQt book suggests writing an updateUi method and calling it manually. I even ended up calling it from a timer once per 0.1 seconds, in order to avoid many manual calls from methods that may update the GUI. Am I missing something? Is there a better way to achieve this?

An example: I have a simple app with a Start button that initiates some processing. The start button should be enabled only when a file has been opened using the menu. In addition, there's a permanent widget on the status bar that displays information.
My application has states:

Before the file is opened (in this state the status bar show something special and the start button is disabled)
File was opened and processing wasn't started: the start button is enabled, status bar shows something else
The processing is running: the start button now says "Stop", and the status bar reports progress

In Wx, I'd have the update UI event of the button handle its state: the text on it, and whether it's enabled, depending on the application state. The same for the status bar (or I'd use EVT_IDLE for that).
In Qt, I have to update the button in several methods that may affect the state, or just create a update_ui method and call it periodically in a timer. What is the more "QT"-ish way?
The use of EVT_UPDATE_UI in wxWidgets seems to highlight one of the fundamental differences in the way wxWidgets and Qt expect developers to handle events in their code.
With Qt, you connect signals and slots between widgets in the user interface, either handling "business logic" in each slot or delegating it to a dedicated method. You typically don't worry about making separate changes to each widget in your GUI because any repaint requests will be placed in the event queue and delivered when control returns to the event loop. Some paint events may even be merged together for the sake of efficiency.
So, in a normal Qt application where signals and slots are used to handle state changes, there's basically no need to have an idle mechanism that monitors the state of the application and update widgets because those updates should occur automatically.
You would have to say a bit more about what you are doing to explain why you need an equivalent to this event in Qt.
wx's idle and UI update events in PyQt