Tornado web server exports methods for escape/unescape html, xml, Json among others. This blog discusses about encoding and decoding JSON format.
Tornado has the following methods:
- tornado.escape.json_encode(value) – JSON’ify the Python object passed to it as argument
- tornado.escape.json_decode(value) – Converts the JSON string into Python Object
Here’s a usage example:
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| <html> | |
| <title> | |
| JSON Example | |
| </title> | |
| <body> | |
| <FORM ACTION="/blog" METHOD=POST> | |
| Title: <input type="text" name="title"> | |
| Author: <input type="text" name="author"> | |
| <input type="submit" value="post" name="Submit"/> | |
| </FORM> | |
| </body> | |
| </html> |
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| import tornado.web | |
| import tornado.escape | |
| import tornado.httpclient | |
| class Blog(tornado.web.RequestHandler): | |
| def get(self): | |
| self.render('jsonform.html') | |
| def post(self): | |
| data_json = tornado.escape.json_encode(self.request.arguments) | |
| self.write(data_json) | |
| ## handles client request | |
| class Language(tornado.web.RequestHandler): | |
| def get(self): | |
| data = {'py':'Python', 'js':'JavaScript'} | |
| self.set_header('Content-Type', 'text/javascript') | |
| self.write(tornado.escape.json_encode(data)) | |
| application = tornado.web.Application([ | |
| (r"/blog", Blog), | |
| (r"/lang", Language), | |
| ], debug=True) | |
| if __name__ == '__main__': | |
| application.listen(8888) | |
| tornado.ioloop.IOLoop.instance().start() |
In this example,
1. When user browses to http://localhost:8888/blog, jsonform.html is rendered that asks for ‘Title’ and ‘Author’
2. On filling this form, a POST request is sent to /blog URL, where the posted arguments are encoded to JSON string with tornado.escape.json_encode() and rendered on the user browser
3. class Language is request handler that caters to http://localhost:8888/lang. In this class, a Python dictionary object is converted to JSON string with tornado.escape.json_encode() and responds with this JSON string to any client request.
4. When tornadojsonclient.py makes a GET request to /lang URL, JSON string is sent as a response. The client decodes this JSON string to a Python dictionary object with tornado.escape.json_decode() method
Code for tornadojsonclient.py below
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| import tornado.httpclient | |
| http = tornado.httpclient.HTTPClient() | |
| response = http.fetch("http://localhost:8888/lang") | |
| data = tornado.escape.json_decode(response.body) | |
| print data['py'], data['js'] |
