def METHOD_NAME(self, label, value):
    """Update flag associated with *label*.
     :raise AttributeError: when *label* is not in use or read-only"""
    if label in PLANTERS:
        raise AttributeError('flag {0} cannot be changed by user'
                                .format(repr(label)))
    flags = self._ag._getFlags(label)
    if flags is None:
        raise AttributeError('flags with label {0} must be set for '
                                'AtomGroup first'.format(repr(label)))
    flags[self._indices] = value