Return an instance of the appropriate shape proxy class for *shape_elm*
    on a slide.

def SlideShapeFactory(shape_elm, parent):
    """
    Return an instance of the appropriate shape proxy class for *shape_elm*
    on a slide.
    """
    if shape_elm.has_ph_elm:
        return _SlidePlaceholderFactory(shape_elm, parent)
    return BaseShapeFactory(shape_elm, parent)