lookupDict = {} searchRows = gp.searchcursor(lookupTbl) searchRow = searchRows.next() while searchRow: lookupDict[searchRow.LOOKUPITEM] = [searchRow.FIELDVALUE1,searchRow.FIELDVALUE2] searchRow = searchRows.next() del searchRow del searchRows updateRows = gp.updatecursor(tableToUpdateTbl) updateRow = updateRows.next() while updateRow: updateRow.MEAN = (lookupDict[updateRow.LOOKUPITEM][0] + lookupDict[updateRow.LOOKUPITEM][1]) / 2 updateRows.UpdateRow(updateRow) updateRow = updateRows.next() del updateRow del updateRows del lookupDict