An WeChat SDK for Official Account written in Python + web.py (run on SAE primely) Author: Jerry Ling

To use this SDK, you will need an account on WeChat's Media-Platform, you can register here. `For short, MP will be refers to Media-Platform from now on. You should have basic knowledge on how WeChat's service works(such as how to auth the server), for more information #####Note: There is certain code in the files written only for Sina SAE, I will point them out in the following explanation.

After your server is verified for MP, the MP server will send every message(include Event such as subscription ) to your server through POST method. And the message will be parsed in the XML format. Here's a XML example for a Text Message:

<xml>
 <ToUserName><![CDATA[toUser]]></ToUserName>
 <FromUserName><![CDATA[fromUser]]></FromUserName> 
 <CreateTime>1348831860</CreateTime>
 <MsgType><![CDATA[text]]></MsgType>
 <Content><![CDATA[a test from user]]></Content>
 <MsgId>1234567890123456</MsgId>
</xml>

And if your server reply the message to the same person(verified using ToUserName and FromUserName) within 5 seconds, and in appropriate format.

Such as a Text reply:

<xml>
    <ToUserName><![CDATA[toUser]]></ToUserName>
    <FromUserName><![CDATA[fromUser]]></FromUserName>
    <CreateTime>12345678</CreateTime>
    <MsgType><![CDATA[text]]></MsgType>
    <Content><![CDATA[hello world]]></Content>
</xml>

Again you can find all these on MP's wiki

The response file in Pychat is:

inter.py

located in the root dictionary.

###Using web.py indexing I used web.py in the SDK to handle the request, and web.py also provides a way to mapping the urls on the server.The file is:

index.wsgi

in the file:

# coding: UTF-8
import os  #nessary for every one
import sae  #is only needed for Sina SAE
import web  #this is web.py
from inter import MpRobot  #from the inter.py import MpRobot class

urls = (            #map the url:/ with the MpRobot class
    '/', 'MpRobot'
)

app_root = os.path.dirname(__file__)  #asign the path for files
templates_root = os.path.join(app_root, 'templates')  #asign the path to templates folder
render = web.template.render(templates_root)  #load web.py render

app = web.application(urls, globals()).wsgifunc()  #These two lines are only needed for Sina SAE to create app on its engine
application = sae.create_wsgi_app(app)             #

If you server located at crap.sae.com.cn, so its url would be http://crap.sae.com.cn/, now it's linked the class MpRobot .

For more information related to web.py, click.

###Using web.py and lxml to process POSTed data

def __init__(self):  
        self.app_root = os.path.dirname(__file__)
        self.templates_root = os.path.join(self.app_root, 'templates') 
        self.render = web.template.render(self.templates_root)
        post_get = web.data()  # get POST data from WeChat
        post_xml = etree.fromstring(post_get)  # process the POST data with lxml
        self.xml_ins = XmlMsg(post_xml.find("ToUserName").text, #creating instance
                              post_xml.find("FromUserName").text,
                              post_xml.find("MsgType").text,
                              post_xml.find("CreateTime").text
        )

You can easily get everything you need in the XML through .find(STRING) method in the post_xml now. ###Send the response Use the XML format mentioned in the I Chapter to response.

##3.(Truly) Tricky Template rendering P.s The thing f***ed me most at first is the template rendering, so don't be upset if it confused you too before reading the doc. For sure there is web.py explanation on template; feel free to check it since I won't go too detailed here.

Check how to load templates dictionary and render in the previous section if you forget how to do so.

Let's see on example of the template .xml file:

$def with (toUser,fromUser,createTime,content) #the args here will be used to take over the variables following 
<xml>
    <ToUserName>
        <![CDATA[$toUser]]> # the $toUser here will be replaced by the toUser above
    </ToUserName>
    <FromUserName>
        <![CDATA[$fromUser]]>
    </FromUserName>
    <CreateTime>
        $createTime
    </CreateTime>
    <MsgType>
        <![CDATA[text]]>
    </MsgType>
    <Content>
        <![CDATA[$:content]]>
    </Content>
</xml>

since we have defined:

self.render = web.template.render(self.templates_root)

When we want to return(reply) in the format, the only thing we need to do is:

return self.render.reply_text("FRomuser",
                              "TOuser",
                              int(time.time()),
                              "CONTENT AS STRING"
        )

and the resultant XML would be:

$def with (toUser,fromUser,createTime,content)
<xml>
    <ToUserName>
        <![CDATA[TOuser]]>
    </ToUserName>
    <FromUserName>
        <![CDATA[FRomuser]]>
    </FromUserName>
    <CreateTime>
        123123 # the time would be int
    </CreateTime>
    <MsgType>
        <![CDATA[text]]>
    </MsgType>
    <Content>
        <![CDATA[CONTENT AS STRING]]>
    </Content>
</xml>

One more thing see how I used:

<![CDATA[$:content]]>

the very ":" is crucial. It means not using HTML escaping. Thus "<" will not be turned into "%3C" in the result. For more on escaping.

##4.Tips

1. The str will just works fine for the result returned to WeChat server, thus if you want to have multiple(and not constant) content, say, items in the news MsgType, you will want to convert the XML into str and then perform the regular manipulation for string.