Python脚本中的SSH隧道卡住了

我需要通过SSH进行隧道访问数据库。使用sshtunnel在Python代码中创建隧道后( https://github.com/pahaz/sshtunnel/ ),脚本挂起,不再执行其他命令。我从提供的代码中看到的最后一个打印是local\u bind\u port。之后的一切都卡住了。我是否误解了一些基本原则?

当我通过cmd行手动创建隧道时,db连接在单独的python脚本中运行良好。

系统:Python 3.6.1,sshtunnel 0.1.2,macOS 10.12,服务器为CentOS 7

import pymysql.cursors
import sshtunnel

with SSHTunnelForwarder(
        ('gateway_host', gateway_port),
        ssh_username='ssh_username',
        ssh_pkey='/path/to/id_rsa',
        ssh_private_key_password='pw',
        remote_bind_address=('remote_bind', 3306),
        local_bind_address=('127.0.0.1', 3306),
        logger=create_logger(loglevel=1)
) as tunnel:
    print('Establishing connection')

    print('tunnel_bindings:', tunnel.tunnel_bindings)
    print('tunnel_is_up:', tunnel.tunnel_is_up)
    print('local_bind_port:', tunnel.local_bind_port)

    connection = pymysql.connect(host='127.0.0.1',
                                 port=3306,
                                 user='db_username',
                                 password='db_password',
                                 db='db_name',
                                 cursorclass=pymysql.cursors.DictCursor)

    try:
        with connection.cursor() as cursor:
            sql = '''SELECT VERSION();'''
            cursor.execute(sql)
            result = cursor.fetchall()
            print(result)
    finally:
        connection.close()

    print('Finish')

日志输出(在最后一行之后卡住):

2017-07-26 22:42:37,788| INF |  Srv-3306/1318@sshtunnel | Opening tunnel: 127.0.0.1:3306 <> remote_bind:3306
tunnel_bindings: {('remote_bind', 3306): ('127.0.0.1', 3306)}
tunnel_is_up: {('127.0.0.1', 3306): True}
local_bind_port: 3306
2017-07-26 22:42:37,864| TRA |  Thread-3/0347@sshtunnel | #1 <-- ('127.0.0.1', 63007) connected

ssh -L 3306:remote_bind:3306 ssh_username@gateway_host -p gateway_port -N

谢谢你的帮助