'The ``<w:tc>`` element appearing at grid column *idx*. Raises
|ValueError| if no ``w:tc`` element begins at that grid column.'

def tc_at_grid_col(self, idx):

    grid_col = 0
    for tc in self.tc_lst:
        if (grid_col == idx):
            return tc
        grid_col += tc.grid_span
        if (grid_col > idx):
            raise ValueError((u'no    cell    on    grid    column    %d' % idx))
    raise ValueError(u'index    out    of    bounds')
