code: def colindex_by_colname(self, colname):
          
          for i, coldef in enumerate(self):    # iterate each column's definition
              if coldef.name == colname:
                  return i
          raise ValueError('No column named "%s" found' % (colname))
docs: Return column index whose name is :param:`column`
  
          :raises: `ValueError` when no column with :param:`colname` found