Subclasses may override this method.

def _set_type(self, value):
        """
        Subclasses may override this method.
        """
        point = self._point
        # convert corner to curve
        if value == "curve" and point.type == "line":
            # This needs to insert off curves without
            # generating unnecessary points in the
            # following segment. The segment object
            # implements this logic, so delegate the
            # change to the corresponding segment.
            segment = self._segment
            segment.type = "curve"
            segment.smooth = True
        # convert curve to corner
        elif value == "corner" and point.type == "curve":
            point.smooth = False