erase lines after drawing them in PyGTK- Cairo

I want to ask how can I erase a line witch I've drawn by using the pyGTK

I used:cairo library

cr = widget.window.cairo_create()
cr.move_to(x, y)
cr.line_to(x1, y1)
cr.stroke()

I want to delete this line after drawing it on screen

You can't delete the line; it's erased anyway during the next expose event, so you just have to wait until the next expose event and then not draw it.