You can specify the minimum and maximum number of steps with set Minimum() and set Maximum.
The current number of steps is set with set Value().
There are a number of similar posts on Py Qt4 progress bars not updating.
They all focus on the issue of threads & where the program actually updates the window.
This is useful, for example, when using QFtp or QNetwork Access Manager to download items when they are unable to determine the size of the item being downloaded. The parent argument, if not None, causes self to be owned by Qt instead of Py Qt. By default, the minimum step value is set to 0, and the maximum to 100. This method is useful for subclasses when they need a QStyle Option Progress Bar or QStyle Option Progress Bar V2, but don't want to fill in all the information themselves. Sets the progress bar's minimum and maximum values to minimum and maximum respectively.