Python Pyro4 - Python Remote Objects

在线文档: http://pythonhosted.org/Pyro4/intro.html

Pyro4，全名Python Remote Object。
学习这个库主要是因为工作需要在Java中调用Python。Pyro库的主要作用是让我们的应用可以在network下相互通信，是个轻量级的库。对于返回值的类型支持强大。并且Pyro是100%用Python写的，兼容任何版本的Python，包括3.x。
Pyro4发布超过15年了，而且现在还在持续更新。

关于Pyro4的特点，上文中的在线文档首页列了27条，就不一一列举了。生产环境有用到，并且没有出现过任何问题。

前提，需要先Install Pyro4 module: 可以通过pip工具进行下载安装。
Mac OS系统自带Python2.7，不过我自己又装了Python3.6，于是对应的pip命令也默认变pip3，具体如下:

>pip3 -V
>pip 9.0.1 from /Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/site-packages (python 3.6)
>pip3 install Pyro4

Log表明已经装好: Successfully installed Pyro4-4.56 serpent-1.19

示例1: python server <---- python client
例子在Pyro4的官网首页上就有，我这里只是拷贝测试下:

Server端代码: # saved as greeting-server.py

import Pyro4

@Pyro4.expose
class GreetingMaker(object):
    def get_fortune(self, name):
        return "Hello, {0}. Here is your fortune message:\n" \
               "Behold the warranty -- the bold print giveth and the fine print taketh away.".format(name)
daemon = Pyro4.Daemon()                # make a Pyro daemon
uri = daemon.register(GreetingMaker)   # register the greeting maker as a Pyro object
print("Ready. Object uri =", uri)      # print the uri so we can use it in the client later
daemon.requestLoop()                   # start the event loop of the server to wait for calls

运行后，输出: Ready. Object uri = PYRO:obj_73fa03c1a27b482195612fcd66357b3a@localhost:58672

客户端: # saved as greeting-client.py

import Pyro4

uri = input("What is the Pyro uri of the greeting object? ").strip()
name = input("What is your name? ").strip()
greeting_maker = Pyro4.Proxy(uri)         # get a Pyro proxy to the greeting object
print(greeting_maker.get_fortune(name))   # call method normally

运行后（若报错Connection refused，请看下文的问题1）:
What is the Pyro uri of the greeting object? PYRO:obj_73fa03c1a27b482195612fcd66357b3a@localhost:58672
What is your name? allen
Hello, allen. Here is your fortune message:
Behold the warranty -- the bold print giveth and the fine print taketh away.


示例2: python server <---- java client
这里用到一个第三方库叫pyrolite-4.10.jar（最新版本是2017-02，v4.18），具体在线资源如下：
Github（大量例子及源码）: https://github.com/irmen/Pyrolite
在线Python文档: http://pythonhosted.org/Pyro4/pyrolite.html
Maven仓库: https://mvnrepository.com/artifact/net.razorvine/pyrolite/4.10

用Maven的话会自动下载依赖，如需要自己添加，需加依赖: serpent-1.12.jar

具体例子，github上有，我拷贝下:
先是服务端（Python）:
注:
1. 比第一个例子中的稍微复杂，是因为使用了name-server（可自定义，比url好记、方便）。
2. 注解@Pyro4.expose表示要暴露的范围，若加在class前面说明里面所有的方法都可以被客户端所调用，若加在单个方法中，那么其它方法对外则不可见。
3. 加了security: hmac，这段代码只是起到安全作用，可不写，具体参见: http://pythonhosted.org/Pyro4/security.html
4. 设了最简单的String参数，当然其它类型的也都可以支持。

import Pyro4

class GreetingMakerJava(object):
    @Pyro4.expose
    def get_fortune(self, name):
        return "Hello, " + name;

daemon = Pyro4.core.Daemon()                # make a Pyro daemond
daemon._pyroHmacKey = b'demokey'

ns = Pyro4.locateNS()                       # find the name server
uri = daemon.register(GreetingMakerJava)    # register the greeting maker as a Pyro object
ns.register("example.greeting", uri)        # register the object with a name in the name server

print("Ready.")
print(list(ns.list(prefix="example.").keys()))
daemon.requestLoop()                        # start the event loop of the server to wait for calls

Java客户端:

import net.razorvine.pyro.Config;
import net.razorvine.pyro.NameServerProxy;
import net.razorvine.pyro.PyroProxy;
public class TestPython {
	public static void main(String[] args) throws Exception {
		Config.METADATA = false; // Pyro4.56 have some bugs to get metadata.
	    NameServerProxy ns = NameServerProxy.locateNS(null);
	    PyroProxy remoteobject = new PyroProxy(ns.lookup("example.greeting"));
	    remoteobject.pyroHmacKey = "demokey".getBytes();
	    Object result = remoteobject.call("get_fortune", "allen");
	    String message = (String)result;
	    System.out.println("result message=" + message);
	    remoteobject.close();
	    ns.close();
	}
}
// result message=Hello, allen

-------------------------------------------------------------------------
使用过程中遇到的问题：

1. 在运行第1个例子的客户端，遇到错误: ConnectionRefusedError: [Errno 61] Connection refused
需要打开python的name service:

>python3 -m Pyro4.naming
Not starting broadcast server for localhost.
NS running on localhost:9090 (127.0.0.1)
Warning: HMAC key not set. Anyone can connect to this server!
URI = PYRO:Pyro.NameServer@localhost:9090

参考: http://stackoverflow.com/questions/34499331/pyro4-failed-to-locate-the-nameserver

2. 在运行第2个例子的客户端，遇到错误: Exception in thread "main" java.lang.ClassCastException: java.util.ArrayList cannot be cast to java.util.HashSet

尝试解决，加上Config.METADATA = false;