Tornado: get request arguments

Question

I have following code:

application = tornado.web.Application([
    (r"/get(.*)", GetHandler),
])

class GetHandler(tornado.web.RequestHandler):
    def get(self, key):
        response = {'key': key}
        self.write(response)

when I go to localhost:port/get?key=python I receive empty key value {'key': ''}. What is wrong here?

Answer 1

(.*) in regex matches everything. So this — (r"/get(.*)", GetHandler) — will match anything followed by /get, example:

/get
/getsomething
/get/something
/get.asldfkj%5E&(*&fkasljf

Let's say a request comes in at localhost:port/get/something, then the value of key argument in GetHandler.get(self, key) will be /something (yes, including the slash because .* matches everything).

But if a request comes in at localhost:port/get?key=python, the value of key argument in GETHandler.get(self, key) will be an empty string. It happens because the part containing ?key=python is called a Query String. It's not part of the url path. Tornado (or almost every other web framework) doesn't pass this to the view as an argument.

---

There are two ways you can change your code:

1. If you want to access your view like this - localhost:port/get?key=python, you'll need to make changes to your url config and to your view:

   application = tornado.web.Application([
       (r"/get", GetHandler),
   ])
   
   class GetHandler(tornado.web.RequestHandler):
       def get(self):
           key = self.get_argument('key', None)
           response = {'key': key}
           self.write(response)
   

2. If you don't want to change your app url config and your view, you'll need to make the request like this - localhost:port/get/python.
   But still you'll need to make a small change to your url config. Add a slash - / - between get and (.*), because otherwise the value of key would be /python instead of python.

   application = tornado.web.Application([
       (r"/get/(.*)", GetHandler), # note the slash
   ])