I basically have the same question as: How to quickly calculate bounding box coordinates of a selected polygon with QGIS. However I am building a stand alone application in python and so do not have the iFace class. I can get to the extent class easily enough with :
box = layer2.extent() OR box = self.map_canvas.extent()
Which gives me an object that claims it is an extent, but how do I get the coordinates out?