- pxa = getattr(a, 'px', xa)
- pya = getattr(a, 'py', ya)
- pxb = getattr(b, 'px', xb)
- pyb = getattr(b, 'py', yb)
+ try: pxa = a.px
+ except KeyError: pxa = xa
+ try: pya = a.py
+ except KeyError: pya = ya
+ try: pxb = b.px
+ except KeyError: pxb = xb
+ try: pyb = b.py
+ except KeyError: pyb = yb