Você pode usar cursores do lado do servidor.
cur = conn.cursor('cursor-name') # server side cursor
cur.itersize = 10000 # how much records to buffer on a client
cur.execute("SELECT * FROM mytable;")
cur = conn.cursor('cursor-name') # server side cursor
cur.itersize = 10000 # how much records to buffer on a client
cur.execute("SELECT * FROM mytable;")
