tornado documentation tornado web server文档, 翻墙所得

Posted by bower on November 17, 2009
linux/ubuntu, python

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FriendFeed‘s web server is a relatively simple,
non-blocking web server written in Python. The FriendFeed application is
written using a web framework that looks a bit like or Google’s
but with additional tools and optimizations to take advantage of the
non-blocking web server and tools.

Tornado is an open source
version of this web server and some of the tools we use most often at
FriendFeed. The framework is distinct from most mainstream web server
frameworks (and certainly most Python frameworks) because it is
non-blocking and reasonably fast. Because it is non-blocking
and uses epoll, it can handle 1000s of simultaneous standing connections,
which means the framework is ideal for real-time web services. We built the
web server specifically to handle FriendFeed’s real-time features —
every active user of FriendFeed maintains an open connection to the
FriendFeed servers. (For more information on scaling servers to support
thousands of clients, see
The C10K problem.)

Here is the canonical “Hello, world” example app:

import tornado.httpserver
import tornado.ioloop
import tornado.web

class MainHandler(tornado.web.RequestHandler):
    def get(self):
        self.write("Hello, world")

application = tornado.web.Application([
    (r"/", MainHandler),

if __name__ == "__main__":
    http_server = tornado.httpserver.HTTPServer(application)

See Tornado walkthrough below for a detailed
walkthrough of the tornado.web package.

We attempted to clean up the code base to reduce interdependencies between
modules, so you should (theoretically) be able to use any of the modules
independently in your project without using the whole package.


Download the most recent version of Tornado from GitHub:


You can also browse the source on GitHub. To install Tornado:

tar xvzf tornado-0.2.tar.gz
cd tornado-0.2
python build
sudo python install

After installation, you should be able to run any of the demos in the demos
directory included with the Tornado package.



Tornado has been tested on Python 2.5 and 2.6. To use all of the features of Tornado, you need to have PycURL and a JSON library like simplejson installed. Complete installation instructions for Mac OS X and Ubuntu are included below for convenience.

Mac OS X 10.5/10.6

sudo easy_install setuptools pycurl== simplejson

Ubuntu Linux

sudo apt-get install python-dev python-pycurl python-simplejson

Module index

The most important module is web, which is the web framework
that includes most of the meat of the Tornado package. The other modules
are tools that make web more useful. See
Tornado walkthrough below for a detailed
walkthrough of the web package.

Main modules

  • web – The web framework on which FriendFeed is built. web incorporates most of the important features of Tornado
  • escape – XHTML, JSON, and URL encoding/decoding methods
  • database – A simple wrapper around MySQLdb to make MySQL easier to use
  • template – A Python-based web templating language
  • httpclient – A non-blocking HTTP client designed to work with web and httpserver
  • auth – Implementation of third party authentication and authorization schemes (Google OpenID/OAuth, Facebook Platform, Yahoo BBAuth, FriendFeed OpenID/OAuth, Twitter OAuth)
  • locale – Localization/translation support
  • options – Command line and config file parsing, optimized for server environments

Low-level modules

  • httpserver – A very simple HTTP server built on which web is built
  • iostream – A simple wrapper around non-blocking sockets to aide common reading and writing patterns
  • ioloop – Core I/O loop

Random modules

  • s3server – A web server that implements most of the Amazon S3 interface, backed by local file storage

Tornado walkthrough

Request handlers and request arguments

A Tornado web application maps URLs or URL patterns to subclasses of
tornado.web.RequestHandler. Those classes define get() or post()
methods to handle HTTP GET or POST requests to that URL.

This code maps the root URL / to MainHandler and the URL pattern
/story/([0-9]+) to StoryHandler. Regular expression groups are passed
as arguments to the RequestHandler methods:

class MainHandler(tornado.web.RequestHandler):
    def get(self):
        self.write("You requested the main page")

class StoryHandler(tornado.web.RequestHandler):
    def get(self, story_id):
        self.write("You requested the story " + story_id)

application = tornado.web.Application([
    (r"/", MainHandler),
    (r"/story/([0-9]+)", StoryHandler),

You can get query string arguments and parse POST bodies with the
get_argument() method:

class MainHandler(tornado.web.RequestHandler):
    def get(self):

' ' ' ' ' '
') def post(self): self.set_header("Content-Type", "text/plain") self.write("You wrote " + self.get_argument("message"))

If you want to send an error response to the client, e.g., 403 Unauthorized,
you can just raise a tornado.web.HTTPError exception:

if not self.user_is_logged_in():
    raise tornado.web.HTTPError(403)

The request handler can access the object representing the current request
with self.request. The HTTPRequest object includes a number of useful
attribute, including:

  • arguments – all of the GET and POST arguments
  • files – all of the uploaded files (via multipart/form-data POST requests)
  • path – the request path (everything before the ?)
  • headers – the request headers

See the class definition for HTTPRequest in httpserver for a complete list
of attributes.


You can use any template language supported by Python, but Tornado ships
with its own templating language that is a lot faster and more flexible
than many of the most popular templating systems out there. See the
template module documentation for complete documentation.

A Tornado template is just HTML (or any other text-based format) with
Python control sequences and expressions embedded within the markup:

      {{ title }}

    {% for item in items %}
  • {{ escape(item) }}
  • {% end %}

If you saved this template as “template.html” and put it in the same
directory as your Python file, you could render this template with:

class MainHandler(tornado.web.RequestHandler):
    def get(self):
        items = ["Item 1", "Item 2", "Item 3"]
        self.render("template.html", title="My title", items=items)

Tornado templates support control statements and expressions. Control
statements are surronded by {% and %}, e.g., {% if len(items) > 2 %}.
Expressions are surrounded by {{ and }}, e.g., {{ items[0] }}.

Control statements more or less map exactly to Python statements. We support
if, for, while, and try, all of which are terminated with {% end %}.
We also support template inheritance using the extends and block
statements, which are described in detail in the documentation for the
template module.

Expressions can be any Python expression, including function calls. We
support the functions escape, url_escape, and json_encode by default,
and you can pass other functions into the template simply by passing them
as keyword arguments to the template render function:

class MainHandler(tornado.web.RequestHandler):
    def get(self):
        self.render("template.html", add=self.add)

    def add(self, x, y):
        return x + y

When you are building a real application, you are going to want to use
all of the features of Tornado templates, especially template inheritance.
Read all about those features in the template module

Under the hood, Tornado templates are translated directly to Python.
The expressions you include in your template are copied verbatim into
a Python function representing your template. We don’t try to prevent
anything in the template language; we created it explicitly to provide
the flexibility that other, stricter templating systems prevent.
Consequently, if you write random stuff inside of your template expressions,
you will get random Python errors when you execute the template.

Cookies and secure cookies

You can set cookies in the user’s browser with the set_cookie method:

class MainHandler(tornado.web.RequestHandler):
    def get(self):
        if not self.get_cookie("mycookie"):
            self.set_cookie("mycookie", "myvalue")
            self.write("Your cookie was not set yet!")
            self.write("Your cookie was set!")

Cookies are easily forged by malicious clients. If you need to set cookies
to, e.g., save the user ID of the currently logged in user, you need to
sign your cookies to prevent forgery. Tornado supports this out of the
box with the set_secure_cookie and get_secure_cookie methods. To use
these methods, you need to specify a secret key named cookie_secret when
you create your application. You can pass in application settings as keyword
arguments to your application:

application = tornado.web.Application([
    (r"/", MainHandler),
], cookie_secret="61oETzKXQAGaYdkL5gEmGeJJFuYh7EQnp2XdTP1o/Vo=")

Signed cookies contain the encoded value of the cookie in addition to a
timestamp and an HMAC signature. If the
cookie is old or if the signature doesn’t match, get_secure_cookie will
return None just as if the cookie isn’t set. The secure version of the
example above:

class MainHandler(tornado.web.RequestHandler):
    def get(self):
        if not self.get_secure_cookie("mycookie"):
            self.set_secure_cookie("mycookie", "myvalue")
            self.write("Your cookie was not set yet!")
            self.write("Your cookie was set!")

User authentication

The currently authenticated user is available in every request handler
as self.current_user, and in every template as current_user. By
default, current_user is None.

To implement user authentication in your application, you need to
override the get_current_user() method in your request handlers to
determine the current user based on, e.g., the value of a cookie.
Here is an example that lets users log into the application simply
by specifying a nickname, which is then saved in a cookie:

class BaseHandler(tornado.web.RequestHandler):
    def get_current_user(self):
        return self.get_secure_cookie("user")

class MainHandler(BaseHandler):
    def get(self):
        if not self.current_user:
        name = tornado.escape.xhtml_escape(self.current_user)
        self.write("Hello, " + name)

class LoginHandler(BaseHandler):
    def get(self):

' 'Name: ' ' ' '
') def post(self): self.set_secure_cookie("user", self.get_argument("name")) self.redirect("/") application = tornado.web.Application([ (r"/", MainHandler), (r"/login", LoginHandler), ], cookie_secret="61oETzKXQAGaYdkL5gEmGeJJFuYh7EQnp2XdTP1o/Vo=")

You can require that the user be logged in using the
Python decorator
tornado.web.authenticated. If a request goes to a method with this
decorator, and the user is not logged in, they will be redirected to
login_url (another application setting). The example above could
be rewritten:

class MainHandler(BaseHandler):
    def get(self):
        name = tornado.escape.xhtml_escape(self.current_user)
        self.write("Hello, " + name)

settings = {
    "cookie_secret": "61oETzKXQAGaYdkL5gEmGeJJFuYh7EQnp2XdTP1o/Vo=",
    "login_url": "/login",
application = tornado.web.Application([
    (r"/", MainHandler),
    (r"/login", LoginHandler),
], **settings)

If you decorate post() methods with the authenticated decorator, and
the user is not logged in, the server will send a 403 response.

Tornado comes with built-in support for third-party authentication schemes
like Google OAuth. See the auth module for more details. Check
out the Tornado Blog example application for a complete example that
uses authentication (and stores user data in a MySQL database).

Cross-site request forgery protection

Cross-site request forgery, or XSRF, is a common problem for personalized web applications. See the
Wikipedia article
for more information on how XSRF works.

The generally accepted solution to prevent XSRF is to cookie every user
with an unpredictable value and include that value as an additional
argument with every form submission on your site. If the cookie and the
value in the form submission do not match, then the request is likely

Tornado comes with built-in XSRF protection. To include it in your site,
include the application setting xsrf_cookies:

settings = {
    "cookie_secret": "61oETzKXQAGaYdkL5gEmGeJJFuYh7EQnp2XdTP1o/Vo=",
    "login_url": "/login",
    "xsrf_cookies": True,
application = tornado.web.Application([
    (r"/", MainHandler),
    (r"/login", LoginHandler),
], **settings)

If xsrf_cookies is set, the Tornado web application will set the _xsrf
cookie for all users and reject all POST requests hat do not contain a
correct _xsrf value. If you turn this setting on, you need to instrument
all forms that submit via POST to contain this field. You can do this with
the special function xsrf_form_html(), available in all templates:

{{ xsrf_form_html() }}

If you submit AJAX POST requests, you will also need to instrument your
JavaScript to include the _xsrf value with each request. This is the
jQuery function we use at FriendFeed for AJAX POST
requests that automatically adds the _xsrf value to all requests:

function getCookie(name) {
    var r = document.cookie.match("\\b" + name + "=([^;]*)\\b");
    return r ? r[1] : undefined;

jQuery.postJSON = function(url, args, callback) {
    args._xsrf = getCookie("_xsrf");
    $.ajax({url: url, data: $.param(args), dataType: "text", type: "POST",
        success: function(response) {
        callback(eval("(" + response + ")"));

Static files and aggressive file caching

You can serve static files from Tornado by specifying the static_path
setting in your application:

settings = {
    "static_path": os.path.join(os.path.dirname(__file__), "static"),
    "cookie_secret": "61oETzKXQAGaYdkL5gEmGeJJFuYh7EQnp2XdTP1o/Vo=",
    "login_url": "/login",
    "xsrf_cookies": True,
application = tornado.web.Application([
    (r"/", MainHandler),
    (r"/login", LoginHandler),
], **settings)

This setting will automatically make all requests that start with /static/
serve from that static directory, e.g., http://localhost:8888/static/foo.png
will serve the file foo.png from the specified static directory. We
also automatically serve /robots.txt and /favicon.ico from the static
directory (even though they don’t start with the /static/ prefix).

To improve performance, it is generally a good idea for browsers to
cache static resources aggressively so browsers won’t send unnecessary
If-Modified-Since or Etag requests that might block the rendering of
the page. Tornado supports this out of the box with static content

To use this feature, use the static_url() method in your templates rather
than typing the URL of the static file directly in your HTML:

      FriendFeed - {{ _("Home") }}

The static_url() function will translate that relative path to a URI
that looks like /static/images/logo.png?v=aae54. The v argument is
a hash of the content in logo.png, and its presence makes the Tornado
server send cache headers to the user’s browser that will make the browser
cache the content indefinitely.

Since the v argument is based on the content of the file, if you update
a file and restart your server, it will start sending a new v value,
so the user’s browser will automatically fetch the new file. If the file’s
contents don’t change, the browser will continue to use a locally cached
copy without ever checking for updates on the server, significantly
improving rendering performance.

In production, you probably want to serve static files from a more
optimized static file server like nginx. You can
configure most any web server to support these caching semantics. Here
is the nginx configuration we use at FriendFeed:

location /static/ {
    root /var/friendfeed/static;
    if ($query_string) {
        expires max;


The locale of the current user (whether they are logged in or not) is
always available as self.locale in the request handler and as locale
in templates. The name of the locale (e.g., en_US) is available as, and you can translate strings with the locale.translate
method. Templates also have the global function call _() available
for string translation. The translate function has two forms:

_("Translate this string")

which translates the string directly based on the current locale, and

_("A person liked this", "%(num)d people liked this", len(people)) % {"num": len(people)}

which translates a string that can be singular or plural based on the value
of the third argument. In the example above, a translation of the first
string will be returned if len(people) is 1, or a translation of the
second string will be returned otherwise.

The most common pattern for translations is to use Python named placeholders
for variables (the %(num)d in the example above) since placeholders can
move around on translation.

Here is a properly localized template:

      FriendFeed - {{ _("Sign in") }}

{{ _("Username") }}
{{ _("Password") }}
{{ xsrf_form_html() }}

By default, we detect the user’s locale using the Accept-Language header
sent by the user’s browser. We choose en_US if we can’t find an appropriate
Accept-Language value. If you let user’s set their locale as a preference,
you can override this default locale selection by overriding get_user_locale
in your request handler:

class BaseHandler(tornado.web.RequestHandler):
    def get_current_user(self):
        user_id = self.get_secure_cookie("user")
        if not user_id: return None
        return self.backend.get_user_by_id(user_id)

    def get_user_locale(self):
        if "locale" not in self.current_user.prefs:
            # Use the Accept-Language header
            return None
        return self.current_user.prefs["locale"]

If get_user_locale returns None, we fall back on the Accept-Language

You can load all the translations for your application using the
tornado.locale.load_translations method. It takes in the name of the
directory which should contain CSV files named after the locales whose
translations they contain, e.g., es_GT.csv or fr_CA.csv. The method
loads all the translations from those CSV files and infers the list of
supported locales based on the presence of each CSV file. You typically
call this method once in the main() method of your server:

def main():
        os.path.join(os.path.dirname(__file__), "translations"))

You can get the list of supported locales in your application with
tornado.locale.get_supported_locales(). The user’s locale is chosen to
be the closest match based on the supported locales. For example, if the
user’s locale is es_GT, and the es locale is supported, self.locale
will be es for that request. We fall back on en_US if no close match
can be found.

See the locale module documentation for detailed information
on the CSV format and other localization methods.

UI modules

Tornado supports UI modules to make it easy to support standard, reusable
UI widgets across your application. UI modules are like special functional
calls to render components of your page, and they can come packaged with
their own CSS and JavaScript.

For example, if you are implementing a blog, and you want to have
blog entries appear on both the blog home page and on each blog entry page,
you can make an Entry module to render them on both pages. First, create
a Python module for your UI modules, e.g.,

class Entry(tornado.web.UIModule):
    def render(self, entry, show_comments=False):
        return self.render_string(
            "module-entry.html", show_comments=show_comments)

Tell Tornado to use using the ui_modules setting in your

class HomeHandler(tornado.web.RequestHandler):
    def get(self):
        entries = self.db.query("SELECT * FROM entries ORDER BY date DESC")
        self.render("home.html", entries=entries)

class EntryHandler(tornado.web.RequestHandler):
    def get(self, entry_id):
        entry = self.db.get("SELECT * FROM entries WHERE id = %s", entry_id)
        if not entry: raise tornado.web.HTTPError(404)
        self.render("entry.html", entry=entry)

settings = {
    "ui_modules": uimodules,
application = tornado.web.Application([
    (r"/", HomeHandler),
    (r"/entry/([0-9]+)", EntryHandler),
], **settings)

Within home.html, you reference the Entry module rather than printing
the HTML directly:

{% for entry in entries %}
  {{ modules.Entry(entry) }}
{% end %}

Within entry.html, you reference the Entry module with the
show_comments argument to show the expanded form of the entry:

{{ modules.Entry(entry, show_comments=True) }}

Modules can include custom CSS and JavaScript functions by overriding
the embedded_css, embedded_javascript, javascript_files, or
css_files methods:

class Entry(tornado.web.UIModule):
    def embedded_css(self):
        return ".entry { margin-bottom: 1em; }"

    def render(self, entry, show_comments=False):
        return self.render_string(
            "module-entry.html", show_comments=show_comments)

Module CSS and JavaScript will be included once no matter how many times
a module is used on a page. CSS is always included in the of the
page, and JavaScript is always included just before the tag
at the end of the page.

Non-blocking, asynchronous requests

When a request handler is executed, the request is automatically finished.
Since Tornado uses a non-blocking I/O style, you can override this default
behavior if you want a request to remain open after the main request handler
method returns using the tornado.web.asynchronous decorator.

When you use this decorator, it is your responsibility to call
self.finish() to finish the HTTP request, or the user’s browser
will simply hang:

class MainHandler(tornado.web.RequestHandler):
    def get(self):
        self.write("Hello, world")

Here is a real example that makes a call to the FriendFeed API using
Tornado’s built-in asynchronous HTTP client:

class MainHandler(tornado.web.RequestHandler):
    def get(self):
        http = tornado.httpclient.AsyncHTTPClient()

    def on_response(self, response):
        if response.error: raise tornado.web.HTTPError(500)
        json = tornado.escape.json_decode(response.body)
        self.write("Fetched " + str(len(json["entries"])) + " entries "
                   "from the FriendFeed API")

When get() returns, the request has not finished. When the HTTP client
eventually calls on_response(), the request is still open, and the response
is finally flushed to the client with the call to self.finish().

If you make calls to asynchronous library functions that require a callback
(like the HTTP fetch function above), you should always wrap your
callbacks with self.async_callback. This simple wrapper ensures that if
your callback function raises an exception or has a programming error,
a proper HTTP error response will be sent to the browser, and the connection
will be properly closed.

For a more advanced asynchronous example, take a look at the chat example
application, which implements an AJAX chat room using
long polling.

Third party authentication

Tornado’s auth module implements the authentication and authorization
protocols for a number of the most popular sites on the web, including
Google/Gmail, Facebook, Twitter, Yahoo, and FriendFeed. The module includes
methods to log users in via these sites and, where applicable, methods to
authorize access to the service so you can, e.g., download a user’s address
book or publish a Twitter message on their behalf.

Here is an example handler that uses Google for authentication, saving
the Google credentials in a cookie for later access:

class GoogleHandler(tornado.web.RequestHandler, tornado.auth.GoogleMixin):
    def get(self):
        if self.get_argument("openid.mode", None):

    def _on_auth(self, user):
        if not user:
        # Save the user with, e.g., set_secure_cookie()

See the auth module documentation for more details.


Web application performance is generally bound by architecture, not frontend
performance. That said, Tornado is pretty fast relative to most popular
Python web frameworks.

We ran a few remedial load tests on a simple “Hello, world” application
in each of the most popular Python web frameworks
(Django,, and
CherryPy) to get the baseline performance of
each relative to Tornado. We used Apache/mod_wsgi for Django and
and ran CherryPy as a standalone server, which was our impression of how
each framework is typically run in production environments. We ran 4
single-threaded Tornado frontends behind an nginx
reverse proxy, which is how we recommend running Tornado in production
(our load test machine had four cores, and we recommend 1 frontend per

We load tested each with Apache Benchmark (ab) on the a separate machine
with the command

ab -n 100000 -c 25 http://10.0.1.x/

The results (requests per second) on a 2.4GHz AMD Opteron processor with
4 cores:

In our tests, Tornado consistently had 4X the throughput of the next fastest
framework, and even a single standalone Tornado frontend got 33% more
throughput even though it only used one of the four cores.

Not very scientific, but at a high level, it should give you a sense that we
have cared about performance as we built Tornado, and it shouldn’t add too
much latency to your apps relative to most Python web development frameworks.

Running Tornado in production

At FriendFeed, we use nginx as a load balancer
and static file server. We run multiple instances of the Tornado web
server on multiple frontend machines. We typically run one Tornado frontend
per core on the machine (sometimes more depending on utilization).

This is a barebones nginx config file that is structurally similar to the
one we use at FriendFeed. It assumes nginx and the Tornado servers
are running on the same machine, and the four Tornado servers
are running on ports 8000 – 8003:

user nginx;
worker_processes 1;

error_log /var/log/nginx/error.log;
pid /var/run/;

events {
    worker_connections 1024;
    use epoll;

http {
    # Enumerate all the Tornado servers here
    upstream frontends {

    include /etc/nginx/mime.types;
    default_type application/octet-stream;

    access_log /var/log/nginx/access.log;

    keepalive_timeout 65;
    proxy_read_timeout 200;
    sendfile on;
    tcp_nopush on;
    tcp_nodelay on;
    gzip on;
    gzip_min_length 1000;
    gzip_proxied any;
    gzip_types text/plain text/html text/css text/xml
               application/x-javascript application/xml
               application/atom+xml text/javascript;

    # Only retry if there was a communication error, not a timeout
    # on the Tornado server (to avoid propagating "queries of death"
    # to all frontends)
    proxy_next_upstream error;

    server {
        listen 80;

        # Allow file uploads
        client_max_body_size 50M;

        location ^~ /static/ {
            root /var/www;
            if ($query_string) {
                expires max;
        location = /favicon.ico {
            rewrite (.*) /static/favicon.ico;
        location = /robots.txt {
            rewrite (.*) /static/robots.txt;

        location / {
            proxy_pass_header Server;
            proxy_set_header Host $http_host;
            proxy_redirect false;
            proxy_set_header X-Real-IP $remote_addr;
            proxy_set_header X-Scheme $scheme;
            proxy_pass http://frontends;

WSGI and Google AppEngine

Tornado comes with limited support for WSGI. However,
since WSGI does not support non-blocking requests, you cannot use any
of the asynchronous/non-blocking features of Tornado in your application
if you choose to use WSGI instead of Tornado’s HTTP server. Some of the
features that are not available in WSGI applications:
@tornado.web.asynchronous, the httpclient module, and the auth module.

You can create a valid WSGI application from your Tornado request handlers
by using WSGIApplication in the wsgi module instead of using
tornado.web.Application. Here is an example that uses the built-in WSGI
CGIHandler to make a valid
Google AppEngine application:

import tornado.web
import tornado.wsgi
import wsgiref.handlers

class MainHandler(tornado.web.RequestHandler):
    def get(self):
        self.write("Hello, world")

if __name__ == "__main__":
    application = tornado.wsgi.WSGIApplication([
        (r"/", MainHandler),

See the appengine example application for a full-featured AppEngine
app built on Tornado.

Caveats and support

Tornado was refactored from the FriendFeed
code base to reduce dependencies. This refactoring may have introduced
bugs. Likewise, because the FriendFeed servers have always run
behind nginx, Tornado has not been
extensively tested with HTTP/1.1 clients beyond Firefox. Tornado
currently does not attempt to handle multi-line headers and some types
of malformed input.

You can discuss Tornado and report bugs on the Tornado developer mailing list.


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