Return a new vector that has been moved towards the given target by 
        the given extent.  The extent should be between 0 and 1.

def get_interpolated(self, target, extent):
        """ Return a new vector that has been moved towards the given target by 
        the given extent.  The extent should be between 0 and 1. """
        result = self.copy()
        result.interpolate(target, extent)
        return result