docs: def example_transform(v, row, row_n, i_s, i_d, header_s, header_d,scratch, errors, accumulator):
      """ An example column transform.
  
      This is an example of a column transform with all of the arguments listed. An real transform
      can omit any ( or all ) of these, and can supply them in any order; the calling code will inspect the
      signature.
  
      When the function is listed as a transform for a column, it is called for every row of data.
  
      :param v: The current value of the column
      :param row: A RowProxy object for the whiole row.
      :param row_n: The current row number.
      :param i_s: The numeric index of the source column
      :param i_d: The numeric index for the destination column
      :param header_s: The name of the source column
      :param header_d: The name of the destination column
      :param scratch: A dict that can be used for storing any values. Persists between rows.
      :param errors: A dict used to store error messages. Persists for all columns in a row, but not between rows.
      :param accumulator: A dict for use in accumulating values, such as computing aggregates.
      :return: The final value to be supplied for the column.
      """
  
      return str(v)+'-foo'