Often times when we're drawing a GUI, we want our GUI to update based on the data changing in our program.  At the start of the program, let's say I've drawn my GUI based on my initial data.  That data will be changing constantly, so how can I redraw my GUI constantly?
You could create a thread to update the GUI constantly, just pass to it references to the graphical widgets that need to be updated
How to start a "drawing loop" in PyQt?