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CHAPTER 24 ■ ■ ■ Project 5: A Virtual Tea Party In this project, you do some serious network programming. In Chapter 14, I showed you how, in general terms; now you get to try it out. You’ll write a chat server—a program that lets several people connect via the Internet and chat with each other in real time. There are many ways to create such a beast in Python. A simple and natural approach might be to use the Twisted framework (discussed in Chapter 14), for example, with the LineReceiver class taking center stage. In this chapter, I stick to the standard libraries, basing the program on the modules asyncore and asynchat. If you’d like, you could try out some of the alternative methods (such as forking or threading) discussed in Chapter 14. What’s the Problem? Online chatting is becoming quite commonplace. There are many chat services of various kinds (IRC, instant messengers, and so forth) available all over the Internet; some of these are even full-fledged text-based virtual worlds (see http://www.mudconnect.com for a long list). If you want to set up a chat server, there are many free server programs you can download and install—but writing one yourself is useful for two reasons: • You learn about network programming. • You can customize it as much as you want. The second point suggests that you can start with a simple chat server and develop it into basically any kind of server (including a virtual world), with all the power of Python at your fingertips. Pretty awesome, isn’t it? Specific Goals Specifically, the program you create must be able to do the following: • Receive multiple connections from different users. • Let the users act in parallel. • Interpret commands such as say or logout. 455
456 CHAPTER 24 ■ PROJECT 5: A VIRTUAL TEA PARTY • Enable each individual session to behave according to the state the user is in (connected, logged in, logging out, and so on). • Be easily extensible. The two things that will require special tools are the network connections and the parallel nature of the program. Useful Tools The only new tools you need in this project are the asyncore module from the standard library and its relative asynchat. I’ll describe the basics of how these work; you can find more details about them in the Python Library Reference (http://python.org/doc/lib/module-asyncore.html and http://python.org/doc/lib/module-asynchat.html). What’s It For? As discussed in Chapter 14, the basic component in a network program is the socket. Sockets can be created directly by importing the socket module and using the functions there. So what do you need asyncore for? The asyncore framework enables you to juggle several users who are connected simultaneously. Imagine a scenario in which you have no special tools for handling this. When you start up the server, it awaits connecting users. When one user is connected, it starts reading data from that user and supplying results through a socket. But what happens if another user is already connected? The second user to connect must wait until the first one has finished. In some cases that will work just fine, but when you’re writing a chat server, the whole point is that more than one user can be connected—how else could users chat with one another? The asyncore framework is based on an underlying mechanism (the select function from the select module, as discussed in Chapter 14) that allows the server to serve all the connected users in a piecemeal fashion. Instead of reading all the available data from one user before going on to the next, only some data is read. Also, the server reads only from the sockets where there is data to be read. This is done again and again, in a loop. Writing is handled similarly. You could implement this yourself using just the modules socket and select, but asyncore and asynchat provide a very useful framework that takes care of the details for you. ■Tip For alternative ways of implementing parallel user connections, see the section “Multiple Connections” in Chapter 14. Preparations The first thing you need is a computer that’s connected to a network (such as the Internet)— otherwise others won’t be able to connect to your chat server. (It is possible to connect to the
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Beginning Python From Novice to Pro
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For Ranveig
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■CHAPTER 23 Project 4: In the New
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viii ■CONTENTS Strings . . . . .
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About the Technical Reviewer ■JER
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Introduction A C program is like a
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CHAPTER 1 ■ ■ ■ Instant Hacki
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CHAPTER 1 ■ INSTANT HACKING: THE
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CHAPTER 4 ■ ■ ■ Dictionaries:
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82 CHAPTER 5 ■ CONDITIONALS, LOOP
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110 CHAPTER 6 ■ ABSTRACTION But w
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124 CHAPTER 6 ■ ABSTRACTION Also,
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140 CHAPTER 7 ■ MORE ABSTRACTION
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CHAPTER 9 ■ MAGIC METHODS, PROPER
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256 CHAPTER 11 ■ FILES AND STUFF
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270 CHAPTER 12 ■ GRAPHICAL USER I
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298 CHAPTER 14 ■ NETWORK PROGRAMM
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314 CHAPTER 15 ■ PYTHON AND THE W
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358 CHAPTER 17 ■ EXTENDING PYTHON
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CHAPTER 18 ■ ■ ■ Packaging Yo
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392 CHAPTER 20 ■ PROJECT 1: INSTA
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APPENDIX A ■ ■ ■ The Short Ve
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558 APPENDIX B ■ PYTHON REFERENCE
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572 APPENDIX C ■ ONLINE RESOURCES
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Index ■Symbols - operator 558 !=
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■INDEX 579 cmd module 252, 501 Cm
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■INDEX 581 get method 74-75 has_k
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■INDEX 583 ■F Factory class twi
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■INDEX 585 finding conflicts 197
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■INDEX 589 localtime function tim
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■INDEX 595 Python C API 365 hand-
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■INDEX 601 TestCase class methods
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■INDEX 603 further exploration 47
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