From the docs:
About keyword arguments
Only optional arguments can be used as keyword arguments.
So, remove pixmap=
:
open_hand_px = QtGui.QPixmap('open_hand.png')
open_hand_px.setMask(open_hand_px.mask())
open_hand_cursor = QtGui.QCursor(open_hand_px)
self.setCursor(open_hand_cursor)