Question

In Tornado, you can link Regexes to RequestHandlers. The matched groups from the Regexes get passed into the RequestHandler’s get() or post() method as arguments.

The problem is, I want to read the values of these matched groups before the get() or post() is called. Does Tornado have a way of accessing these matched groups outside of get() or post()? I want something analogous to RequestHandler.arguments.

Answer 1

Unfortunately, there does not seem to be a way to access the url regex match from “prepare”.

Looking at the code in tornado/web.py, especially line 949, prepare is called without parameters at all.

I’ve hacked together a solution, that works, but it’s not robust at all… Here it is.

import tornado.ioloop
import tornado.web
from tornado import escape

class MainHandler(tornado.web.RequestHandler):
    def prepare(self):
        # work out url regex match as in
        # tornado/web.py:1283
        handlers = self.application._get_host_handlers(self.request)
        for spec in handlers:
            match = spec.regex.match(self.request.path)
            def unquote(s):
                if s is None: return s
                return escape.url_unescape(s, encoding=None)
            args = [unquote(s) for s in match.groups()]
            # do something with args

    def get(self, who):
        self.write('hello ' + who)

if __name__ == "__main__":
    application = tornado.web.Application([
        (r"/(\w+)", MainHandler),
    ])
    application.listen(8999)
    tornado.ioloop.IOLoop.instance().start()