'Returns the column reference of given column in the grid by its name.
Raises an error if the column name is not in the grid. Otherwise,
returns the fid:uid pair, which may be the empty string.'

def get_column_reference(self, column_name):

    column_id = None
    for column in self._columns:
        if (column.name == column_name):
            column_id = column.id
            break
    if (column_id is None):
        col_names = []
        for column in self._columns:
            col_names.append(column.name)
        raise exceptions.PlotlyError("Whoops,    that    column    name    doesn't    match    any    of    the    column    names    in    your    grid.    You    must    pick    from    {cols}".format(cols=col_names))
    return column_id
