import cx_Oracle
import time

user = 'myuser'
psw = 'admin'
host = '165.45.12.1'
name = 'db'
table = "mytabla"

con = None
cursor = None

try:

    con, cursor = reconectar(con, cursor, user, psw, host, name)

    while True:

        if cursor is not None:
            try:
                query = f'SELECT * FROM {table}'
                cursor.execute(query)
                result = cursor.fetchall()
                print(result)
                print(con)
                print(cursor)
            except (cx_Oracle.DatabaseError, cx_Oracle.InterfaceError) as ex:
                print(f'Excepcion: {ex}')
                print(con)
                print(cursor)
                error, = ex.args
                if error.code == 3135:
                    con, cursor = reconectar(con, cursor, user, psw, host, name)

        time.sleep(20)
except KeyboardInterrupt:
    exit(0)

def reconectar(con, cursor, user, psw, host, name):

    try:
        cursor.close()
    except Exception:
        print("Cursor ya cerrado")

    try:
        con.close()
    except Exception:
        print("Conexión ya cerrada")

    try:
        con = cx_Oracle.connect(user+'/'+psw+'@'+host+'/'+name)
    except Exception:
        print("Fallo al conectar")
        con = None

    try:
        cursor = con.cursor()
    except Exception:
        print("Fallo al crear cursor")
        cursor = None

    return con, cursor

Cursor ya cerrado
Conexión ya cerrada
[(2, 5, 5, 5, 2, 10, 3, 3, 30, 10, 30, 60, 30, 30, 30, 30, 10.0)]
<cx_Oracle.Connection to myuser@165.45.12.1/db>
<cx_Oracle.Cursor on <cx_Oracle.Connection to myuser@165.45.12.1/db>>
Excepcion: ORA-03135: la conexión ha perdido contacto
Identificador de Proceso: 0
Identificador de Sesión: 842 Número de Serie: 98425
<cx_Oracle.Connection to myuser@165.45.12.1/db>
<cx_Oracle.Cursor on <cx_Oracle.Connection to myuser@165.45.12.1/db>>
[(2, 5, 5, 5, 2, 10, 3, 3, 30, 10, 30, 60, 30, 30, 30, 30, 10.0)]