from robofab.world import CurrentGlyph
myGlyph = CurrentGlyph()
myPen = myGlyph.getPen()

myPen.moveTo((-10,0))
myPen.lineTo((500,0))
myPen.lineTo((500,50))
myPen.lineTo((-10,50))
myPen.lineTo((-10,0))
myPen.closePath()

myGlyph.update()