Building web applications is one of the most common uses of Python. With a plethora of different web frameworks aiming at varying audiences, it has become a rather simple and well-documented process to develop web applications and web services. So popular it has become that the WSGI specification is the industry standard protocol for developing web applications with Python. But the WSGI standard is lacking with two major limitations: It supports only the ‘traditional’ synchronous http request-response cycle thus creating a ‘glass ceiling’ with the amount of requests a single server can handle – often described as the C10K problem. It does not provide an easy and efficient way of developing two-way communication between servers and clients. Often referred to as the real-time web this capability has become increasingly popular with modern web applications. Over the past decade multiple networking libraries have been developed to address these limitations. In this talk we will explore: What is an asynchronous web server and how it differs from other, WSGI-based web servers. What is concurrency and how it can help us achieve supreme performance and scalability in our web applications. We will survey noteworthy libraries which will help achieve true concurrency. How to develop real-time communication, using web sockets, with our Javascript application Concerns, limitations and pitfalls when developing asynchronous web applications.

1. A practical introduction for web developers
Asynchronous IO and The Real-Time Web
EuroPython 2017

2. I am Amit Nabarro
From Israel
Work for
Let out @amitnabarro

3. The State Of Web Development In Python

4. A Common Ground
Web Server Gateway Interface (WSGI)
Est. 2003

5. Web
sever
WSGI Your App
An abstraction layer between your App and
the production web server

6. What's wrong with
WSGI ?
• It's Synchronous
• Supports only HTTP

8. How do we solve this problem ?
Your
App
Your
App
Your
App
Your
App
Your
App
Your
App
We Scale !

9. WSGI only supports HTTP
Which is a stateless protocol
Client Server

10. The Solution …
CONCURRENCY

11. – Wikipedia
“Concurrent computing is a form of
computing in which several computations are
executed during overlapping time periods—
concurrently—instead of sequentially (one
completing before the next starts)”

12. Most Web Apps Mainly Perform IO Operations
Statement:
Parse request
Fetch data
Prepare response
Parse request
Fetch data
Prepare response
Parse request
Fetch data
Prepare response
Parse request
Fetch data
Prepare response

13. Let's do this instead

15. The secret ingredient is giving up control …..

16. $.get(url, function(data){
Do.Something(data);
});
Do.Something.Else();
data = await FetchData()
Do.Something(data)
Do.Something.Else()
Javascript 5 Python 3.5

17. Event Loop: What Is It ?
File System
Datastore
Computation
Operations
Requests
EVENT LOOP
Single thread

18. WebSockets
“WebSocket is a computer communications
protocol, providing full-duplex communication
channels over a single TCP connection”
Wikipedia

19. Client Server
Handshake (http upgrade)
Connection established
Bi directional messages
Open persistent connection
One side closes the connection
Connection closed
WebSockets

20. Technologies for writing concurrent code in Python
1. Twisted
2. Tornado
3. LibEvent
4. Asyncio
1. Tornado
2. Aiohttp
3. Django-channels
4. Sanic
Libraries Frameworks

21. Advantages
• Efficiency
• Solves the C10K problem
• Spawn tasks easily
• WebSocket connections

22. Pitfalls
• Harder to debug
• Harder to test
• Locks and race conditions
• Concurrent code all the way