@classmethod
def from_atom(class_, atom, pos=None, _offset=None):
    """Create a Col definition from a PyTables atom.

        An optional position may be specified as the pos argument.

        """
    prefix = atom.prefix()
    kwargs = atom._get_init_args()
    colclass = class_._class_from_prefix[prefix]
    return colclass(pos=pos, _offset=_offset, **kwargs)
