Briefly about a cool library for creating web applications in Python — Tornado
Let's install Tornado:
pip install tornadoMain components of Tornado
RequestHandler and request processing
RequestHandler — is the main class in Tornado for handling HTTP requests. Each request is handled by an instance of the class RequestHandlerwhich performs the necessary actions and generates a response.
Example:
import tornado.ioloop
import tornado.web
class MainHandler(tornado.web.RequestHandler):
def get(self):
self.write("Hello, world")
def post(self):
name = self.get_argument('name')
self.write(f"Hello, {name}")
def make_app():
return tornado.web.Application([
(r"/", MainHandler),
])
if __name__ == "__main__":
app = make_app()
app.listen(8888)
tornado.ioloop.IOLoop.current().start()MainHandler processes GET and POST requests. Method get returns the string “Hello, world”, and the method post takes an argument name from the request body and returns a personalized greeting.
RequestHandler contains many useful methods for working with HTTP requests and generating responses:
get_argument(name, default=None, strip=True)— gets an argument from the query string or request body.get_arguments(name, strip=True)— receives a list of arguments.write(chunk)– writes data in response.render(template_name, **kwargs)— renders an HTML template with the passed parameters.set_header(name, value)— sets the HTTP header.set_status(status_code, reason=None)— sets the response status.
Routing
Routing in Tornado is configured using a class Applicationwhich associates URL patterns with the corresponding handlers.
Example:
import tornado.ioloop
import tornado.web
class MainHandler(tornado.web.RequestHandler):
def get(self):
self.write("This is the main page")
class AboutHandler(tornado.web.RequestHandler):
def get(self):
self.write("This is the about page")
def make_app():
return tornado.web.Application([
(r"/", MainHandler),
(r"/about", AboutHandler),
])
if __name__ == "__main__":
app = make_app()
app.listen(8888)
tornado.ioloop.IOLoop.current().start()Here two routes are defined: the root URL (“/”) is processed MainHandlerand the URL “/about” is processed AboutHandler.
Routing in Tornado is defined using a list of tuples, where each tuple contains a URL pattern and a corresponding handler:
application = tornado.web.Application([
(r"/", MainHandler),
(r"/about", AboutHandler),
])Templates
Tornado supports a templating system for generating dynamic HTML pages. Templates allow you to separate the application logic from the presentation.
Example:
import tornado.ioloop
import tornado.web
class MainHandler(tornado.web.RequestHandler):
def get(self):
self.render("index.html", title="Home Page", items=["Item 1", "Item 2", "Item 3"])
def make_app():
return tornado.web.Application([
(r"/", MainHandler),
], template_path="templates")
if __name__ == "__main__":
app = make_app()
app.listen(8888)
tornado.ioloop.IOLoop.current().start()Sample index.html:
<!DOCTYPE html>
<html>
<head>
<title>{{ title }}</title>
</head>
<body>
<h1>{{ title }}</h1>
<ul>
{% for item in items %}
<li>{{ item }}</li>
{% end %}
</ul>
</body>
</html>
Here MainHandler uses the method render to generate an HTML response based on a template index.htmlpassing variables into it title And items.
Tornado uses its own template language, which includes basic constructs for data insertion, loops, and conditionals. Templates are stored in a separate directory specified in the parameter template_path when creating an application.
Asynchronous Programming in Tornado
Asynchronous programming is a feature of Tornado that allows you to create scalable web applications. Tornado uses non-blocking I/O and an event loop to handle large numbers of simultaneous connections.
Asynchronous I/O allows other tasks to be processed while waiting for I/O operations to complete. Tornado uses an event loop that continuously checks for events and runs the appropriate handlers.
Example with event loop:
import tornado.ioloop
import tornado.web
class MainHandler(tornado.web.RequestHandler):
async def get(self):
await self.some_async_function()
self.write("Hello, world")
async def some_async_function(self):
await tornado.gen.sleep(1)
def make_app():
return tornado.web.Application([
(r"/", MainHandler),
])
if __name__ == "__main__":
app = make_app()
app.listen(8888)
tornado.ioloop.IOLoop.current().start()Here some_async_function performs an asynchronous operation sleep for one second. Method get waits for this function to complete before sending a response.
Coroutines and Futures
A coroutine can be thought of as a function that can be paused and resumed. Tornado uses the module to work with coroutines. tornado.gen:
import tornado.ioloop
import tornado.web
import tornado.gen
import asyncio
class MainHandler(tornado.web.RequestHandler):
@tornado.gen.coroutine
def get(self):
result = yield self.some_async_function()
self.write(f"Result: {result}")
@tornado.gen.coroutine
def some_async_function(self):
yield tornado.gen.sleep(1)
return "Async operation complete"
def make_app():
return tornado.web.Application([
(r"/", MainHandler),
])
if __name__ == "__main__":
app = make_app()
app.listen(8888)
tornado.ioloop.IOLoop.current().start()We use tornado.gen.coroutine to define coroutines.some_async_function performs an asynchronous operation and returns the result.
Examples of asynchronous operations:
Asynchronous operations in Tornado include working with HTTP requests, databases, and other external resources.
Asynchronous HTTP request:
import tornado.ioloop
import tornado.web
import tornado.httpclient
class MainHandler(tornado.web.RequestHandler):
async def get(self):
http_client = tornado.httpclient.AsyncHTTPClient()
response = await http_client.fetch("http://example.com")
self.write(response.body)
def make_app():
return tornado.web.Application([
(r"/", MainHandler),
])
if __name__ == "__main__":
app = make_app()
app.listen(8888)
tornado.ioloop.IOLoop.current().start()This is how you can make an asynchronous HTTP request using AsyncHTTPClient.
Asynchronous work with the database:
import tornado.ioloop
import tornado.web
import aiomysql
class MainHandler(tornado.web.RequestHandler):
async def get(self):
pool = await aiomysql.create_pool(host="127.0.0.1", port=3306,
user="root", password='',
db='test', loop=tornado.ioloop.IOLoop.current().asyncio_loop)
async with pool.acquire() as conn:
async with conn.cursor() as cur:
await cur.execute("SELECT 42;")
result = await cur.fetchone()
self.write(f"Result: {result[0]}")
def make_app():
return tornado.web.Application([
(r"/", MainHandler),
])
if __name__ == "__main__":
app = make_app()
app.listen(8888)
tornado.ioloop.IOLoop.current().start()We use aiomysql to perform an asynchronous query to a MySQL database.
Other Tornado Features
WebSocket
Tornado has built-in WebSocket support. Example:
import tornado.ioloop
import tornado.web
import tornado.websocket
class MainHandler(tornado.web.RequestHandler):
def get(self):
self.write("Hello, WebSocket")
class EchoWebSocket(tornado.websocket.WebSocketHandler):
def open(self):
print("WebSocket opened")
def on_message(self, message):
self.write_message(u"You said: " + message)
def on_close(self):
print("WebSocket closed")
def make_app():
return tornado.web.Application([
(r"/", MainHandler),
(r"/websocket", EchoWebSocket),
])
if __name__ == "__main__":
app = make_app()
app.listen(8888)
tornado.ioloop.IOLoop.current().start()Created a simple WebSocket server that sends echo messages back to the client. Class EchoWebSocket inherited from tornado.websocket.WebSocketHandler and overrides methods open, on_message And on_close to handle WebSocket events.
Integration with authentication and authorization frameworks
Tornado supports integration with various authentication and authorization frameworks, including OAuth and OpenID.
Example with OAuth:
import tornado.ioloop
import tornado.web
import tornado.auth
class GoogleLoginHandler(tornado.web.RequestHandler, tornado.auth.GoogleOAuth2Mixin):
async def get(self):
if self.get_argument("code", False):
user = await self.get_authenticated_user(
redirect_uri='http://your.site.com/auth/google',
code=self.get_argument("code"))
self.set_secure_cookie("user", tornado.escape.json_encode(user))
self.redirect("/")
else:
self.authorize_redirect(
redirect_uri='http://your.site.com/auth/google',
client_id=self.settings["google_oauth"]["key"],
scope=['profile', 'email'],
response_type="code",
extra_params={'approval_prompt': 'auto'})
def make_app():
return tornado.web.Application([
(r"/auth/google", GoogleLoginHandler),
], google_oauth={"key": "YOUR_CLIENT_ID", "secret": "YOUR_CLIENT_SECRET"}, cookie_secret="YOUR_COOKIE_SECRET")
if __name__ == "__main__":
app = make_app()
app.listen(8888)
tornado.ioloop.IOLoop.current().start()The user is redirected to the Google login page and then returned with an authentication token.
International support and localization
Tornado provides built-in tools to support i18n internationalization and localization.
Example code for loading and using locales:
import tornado.ioloop
import tornado.web
import tornado.locale
class MainHandler(tornado.web.RequestHandler):
def get(self):
user_locale = self.get_user_locale()
greeting = self.locale.translate("Hello")
self.write(greeting)
def make_app():
tornado.locale.load_translations("locale/")
tornado.locale.set_default_locale('en_US')
return tornado.web.Application([
(r"/", MainHandler),
])
if __name__ == "__main__":
app = make_app()
app.listen(8888)
tornado.ioloop.IOLoop.current().start()Loading translation files from the directory localeand then we use the method translate to get a translated string based on the user's current locale.
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