How to share data between requests in Tornado Web

python tornado
RevMoon picture RevMoon · Sep 3, 2012 · Viewed 8.1k times · Source

I have the following use case for my Tornado web server:

Upon POST requests entries can be made to the server, entries which will not be persisted to a file or database. Upon GET requests a process can be started or terminated.

Hence I need to share data between different requests in my RequestHandler implementation. What is the normal way to do so?

I had difficulties saving data to self, for instance self.entry = "...". In another request the data was not present anymore.

The only working solution I've found is to store that in the application object:

    application = web.Application([
            (r'.*', MainHandler,
            ])

and

    def get(self):
         # ...
         self.application.entry = "..."

Is that the proper way? Also what about synchronization here, I mean this means access to shared data.

Answer

Konrad Reiche picture Konrad Reiche · Sep 3, 2012

I suggest the following: Instead of a database access object pass an object which stores your data, for instance:

data = DataStore()

application = web.Application([
        (r'.*', MainHandler, dict(data = data),
        ])

with the following RequestHandler initialization method.

def initialize(self, data):
     self.data = data

You have to create the object before and pass it, otherwise it will be recreated every time a request is processed.

Related questions

When to use Tornado, when to use Twisted / Cyclone / GEvent / other

Which of these frameworks / libraries would be the best choise for building modern multiuser web application? I would love to have an asynchronous webserver which will allow me to scale easly. What solution will give the best performance / scalability / most …

Read More
Tornado URL query parameters

I've been playing around with Tornado, and I've written some code that doesn't seem very nice. I'm writing an app to store recipes as an example. These are my handlers: handlers = [ (r"/recipes/", RecipeHandler), (r"/recipes", RecipeSearchHandler), #so query params …

Read More
How can I periodically execute a function with asyncio?

I'm migrating from tornado to asyncio, and I can't find the asyncio equivalent of tornado's PeriodicCallback. (A PeriodicCallback takes two arguments: the function to run and the number of milliseconds between calls.) Is there such an equivalent in asyncio? If …

Read More