Você não precisa mais importar o cx_Oracle. A versão mais recente do módulo sqlalchemy chama a função cx_Oracle.makedsn(). Dar uma olhada:
from sqlalchemy.engine import create_engine
DIALECT = 'oracle'
SQL_DRIVER = 'cx_oracle'
USERNAME = 'your_username' #enter your username
PASSWORD = 'your_password' #enter your password
HOST = 'subdomain.domain.tld' #enter the oracle db host url
PORT = 1521 # enter the oracle port number
SERVICE = 'your_oracle_service_name' # enter the oracle db service name
ENGINE_PATH_WIN_AUTH = DIALECT + '+' + SQL_DRIVER + '://' + USERNAME + ':' + PASSWORD +'@' + HOST + ':' + str(PORT) + '/?service_name=' + SERVICE
engine = create_engine(ENGINE_PATH_WIN_AUTH)
#test query
import pandas as pd
test_df = pd.read_sql_query('SELECT * FROM global_name', engine)
