code: def _format_line(headers, fields):
    
    assert len(fields) == len(headers), (fields, headers)
    fields = ["%2.4f" % field if isinstance(field, float) else str(field)
              for field in fields]
    return '  '.join(' ' * max(0, len(header) - len(field)) + field
                     for (header, field) in zip(headers, fields))
docs: Format a line of a table.
  
    Arguments:
      headers: A list of strings that are used as the table headers.
      fields: A list of the same length as `headers` where `fields[i]` is
        the entry for `headers[i]` in this row. Elements can be of
        arbitrary types. Pass `headers` to print the header row.
  
    Returns:
      A pretty string.