def METHOD_NAME(self, index):
    """Set the coordinate set at *index* active."""
    if self._ag._coords is None:
        raise AttributeError('coordinates are not set')
    if not isinstance(index, Integral):
        raise TypeError('index must be an integer')
    n_csets = self._ag._n_csets
    if n_csets <= index or n_csets < abs(index):
        raise IndexError('coordinate set index is out of range')
    if index < 0:
        index += n_csets
    self._acsi = index