def from_list(cells):
        """
        Make a non-bag iterable of cells into a Bag. Some magic may be lost,
        especially if it's zero length.
        TODO: This should probably be part of the core __init__ class.
        TODO: Don't do a piece-by-piece insertion, just slap the whole listed
              iterable in, because this is slow.
        """  # TODO
        bag = Bag(table=None)
        for i, cell_bag in enumerate(cells):
            bag.add(cell_bag._cell)
            if i == 0:
                bag.table = cell_bag.table
            else:
                assert bag.table == cell_bag.table
        return bag