title: Progress bar for event with unknown duration (PySide)
body: <p>I have a GUI developed using PySide. I have a long operation to perform from the interface, but there is no way to predict how long the operation will be. I'd like to display something to the user to tell him: the operation is in progress, please wait. Something like an infinite progress bar, or a spinning wheel. Is there a widget for such operation in Qt? I found the QProgressDialog (and QProgressBar), but it's not appropriate since I cannot predict the amount of work to perform.</p>