def METHOD_NAME(self):
    """Get the distance between a port and its anchor particle.
    If the port has no anchor particle, returns None.
    """
    if self.anchor:
        return np.linalg.norm(self.center - self.anchor.pos)
    else:
        warn(
            "This port is not anchored to another particle. Returning a "
            "separation of None"
        )
        return None