call erlang functions from python

Problem:

In my project, I need to call erlang functions inside python to fulfil some concurrent computing tasks.

在我的项目中,我需要调用erlang方法在python实现一些并行计算任务。

Solution:

module implement the erlang nodes protocol and use python twisted network engine. Now, it is possible to call erlang nodes in python scripts.

Twotp模块实现了erlang节点协议和python Twisted 网络引擎的使用。现在,可以在python脚本中调用erlang节点。

I also found an example . Unfortunately, there are errors in the python sources codes when you make remote procedure call from twotp.NodeClientFactory. I followed the examples with the twotp source codes, and make the rpc from twotp.Process. This works.

在这里我还发现了一个例子。不幸的是从twotp.NodeClientFactory远程过程调用时，python源码中出现了错误。我遵循twotp源码，通过twotp.Process实现rpc协议。

Step 1: Setup erlang nodes.

第一步：安装erlang节点。

%% Demo erlang program.
%% Return hello message.

-module(demo).
-export([hello/1, ping/0, start/0]).

%% Hello function, return hello message.
hello(Name) ->
    Message = "Hello, " ++ Name,
    io:format(Message ++ "~n", []),
    Message.

%% ping loop, return the ping count.
ping_loop(N) ->
    receive
        {get_id, From} ->
            From ! {pong, N},
            ping_loop(N+1)
    end.

%% ping function.
ping() ->
    pingsrv ! {get_id, self()},
    receive
        {pong, N} -> ok
    end,
    {pong, N}.

%% start the server.
start() ->
    Pid = spawn_link(fun() -> ping_loop(1) end),
    register(pingsrv, Pid).

 

Run the erlang program on “test” node.

运行erlang程序在“测试”节点。

$ erl -sname test@localhost
(test@localhost)1> demo:start().
true

 

Step 2: Make rpc call in python.

第二步：在python调用rpc

 

#!/usr/bin/env python
#-*- coding: utf-8 -*-
#
# BSD License
# Copyright (c) 2011, Wang Qiang
# All rights reserved.

"""
Main python program.
I will call erlang function here.
"""
import sys
import twotp
from twisted.internet import reactor

def error(e):
    """
    errback for twisted defered.
    """
    print 'Error:'
    print e
    reactor.stop()

def do_pingpong(process, remote):
    """
    rpc for demo:ping.
    """
    def handle_pong(result):
        """
        callback for handling the demo:ping result.
        """
        text, id_ = result[0].text, result[1]
        print "Got ping result: %s %d" % (text, id_)
        reactor.callLater(1, do_pingpong, process, remote)
    # Make rpc with two.Process.callRemote.
    # call demo:ping() in remote node.
    d = process.callRemote(remote, 'demo', 'ping')
    d.addCallback(handle_pong)
    d.addErrback(error)

def call_hello(process, remote, name):
    """
    rpc for demo:hello.
    """
    def handle_hello(result):
        """
        callback for handling the demo:hello result.
        """
        print "Got hello results", result
        text = ''.join(chr(c) for c in result).decode('latin1')
        print 'String form:', text
        do_pingpong(process, remote)
    # Make rpc with two.Process.callRemote.
    # call demo:hello() with name arg in remote node.
    d = process.callRemote(remote, 'demo', 'hello', name)
    d.addCallback(handle_hello)
    d.addErrback(error)

def main():
    # get the erlang node name
    remote = sys.argv[1]
    # additional args.
    name = sys.argv[2]
    # get the erlang node cookie and setup the twotp.Process.
    cookie = twotp.readCookie()
    this_node = twotp.buildNodeName('demo_client')
    process = twotp.Process(this_node, cookie)
    # start twisted reactor.
    reactor.callWhenRunning(call_hello, process, remote, name)
    reactor.run()

if __name__ == "__main__":
    main()

Run python script and make it works.

运行python脚本并且使他工作。

 

$ python main.py 'test' WangQiang
Got hello results [72, 101, 108, 108, 111, 44, 32, 87, 97, 110, 103, 81, 105, 97, 110, 103]
String form: Hello, WangQiang
Got ping result: pong 2
Got ping result: pong 3
Got ping result: pong 4
Got ping result: pong 5
Got ping result: pong 6
Got ping result: pong 7
Got ping result: pong 8
Got ping result: pong 9
Got ping result: pong 10

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