'Add component to a shape of type compound.
Arguments: poly is a polygon, i. e. a tuple of number pairs.
fill is the fillcolor of the component,
outline is the outline color of the component.
call (for a Shapeobject namend s):
--   s.addcomponent(((0,0), (10,10), (-10,10)), "red", "blue")
Example:
>>> poly = ((0,0),(10,-5),(0,10),(-10,-5))
>>> s = Shape("compound")
>>> s.addcomponent(poly, "red", "blue")
>>> # .. add more components and then use register_shape()'

def addcomponent(self, poly, fill, outline=None):

    if (self._type != 'compound'):
        raise TurtleGraphicsError(('Cannot    add    component    to    %s    Shape' % self._type))
    if (outline is None):
        outline = fill
    self._data.append([poly, fill, outline])
