code: def make_summary_funcs(rows, ids):
      
      return {
          'len': len,
          'list': lambda *x: filter(None, list(x)),
          'max': max,
          'min': min,
          'rows': partial(summary_rows, rows, ids),
          'sum': sum,
          'trace': print_trace
      }
docs: Functions available for listing summary fields.