'Position can be set either as an index referring to the sample number or
the position 0.0 - 1.0
If *rotate* is True, then the item rotates to match the tangent of the curve.'

def __init__(self, curve, index=0, pos=None, rotate=True):

    GraphicsObject.__init__(self)
    self._rotate = rotate
    self.curve = weakref.ref(curve)
    self.setParentItem(curve)
    self.setProperty('position', 0.0)
    self.setProperty('index', 0)
    if hasattr(self, 'ItemHasNoContents'):
        self.setFlags((self.flags() | self.ItemHasNoContents))
    if (pos is not None):
        self.setPos(pos)
    else:
        self.setIndex(index)
