You need create a cursor, then execute the instruction "fetchall()" and assign the result to a variable. Finally you can manipulate the collection of tuples:

sql=" select * from table "

cursor=conn_local.cursor()
cursor.execute(sql)
datos=cursor.fetchall()
cursor.close()
conn_local.close()

#Manipulation of the collection of tuples

if len(datos) > 0:

    for indice in range(len(datos)):
        fila= datos[indice]
        mensaje_salida=mensaje_salida + fila