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CHAPTER 23 ■ ■ ■ Project 4: In the News In this project, you see how you go from a simple prototype without any form of abstraction (no functions, no classes) to a generic system in which some important abstractions have been added. Also, you get a brief introduction to the nntplib library. WHAT IS NNTP? Network News Transfer Protocol (NNTP) is a standard network protocol for managing messages posted on Usenet discussion groups. NNTP servers form a global network that collectively manage these newsgroups, and through an NNTP client (also called a newsreader) you can post and read messages. Most recent Web browsers include NNTP clients, and separate clients exist as well. For more information about Usenet, you may check out the informational Web site at http:// www.usenet.org. What’s the Problem? The program you write in this project will be an information-gathering agent, a program that will be able to gather information (more specifically, news) and compile a report for you. Given the network functionality you have already encountered, that might not seem very difficult— and it isn’t, really. But in this project you go a bit beyond the simple “download a file with urllib” approach. You use another network library that is a bit more difficult to use than urllib, namely nntplib. In addition, you get to refactor the program to allow many types of news sources and various types of destinations, making a clear separation between the front-end and the backend, with the main engine in the middle. ■Note Refactoring means improving the design of an existing program, usually by adding abstraction and structure. 439
440 CHAPTER 23 ■ PROJECT 4: IN THE NEWS Specific Goals The main goals for the final program are as follows: • The program should be able to gather news from many different sources. • It should be easy to add new news sources (and even new kinds of sources). • The program should be able to dispatch its compiled news report to many different destinations, in many different formats. • It should be easy to add new destinations (and even new kinds of destinations). Useful Tools In this project, there is no need to install separate software. What you need, however, are some standard library modules, including one that you haven’t seen before, nntplib, which deals with NNTP servers. Instead of explaining all the details of that module, let’s examine it through some prototyping. You will also be using the time module. See Chapter 10 for more information. Preparations To be able to use nntplib you need to have access to an NNTP server. If you’re not sure whether you do, you could ask your ISP or system administrator for details. In the code examples in this chapter, I use the newsgroup comp.lang.python.announce, so you should make sure that your news (NNTP) server has that group, or you should find some other group you’d like to use. It is important that the NNTP server support the NEWNEWS command—if it doesn’t, the programs in this chapter won’t work. (If you don’t know whether your server supports this command or not, simply try to execute the programs and see what happens.) If you don’t have access to an NNTP server, or your server’s NEWNEWS command is disabled, several open servers are available for anyone to use. A quick Web search for “free nntp server” ought to give you a number of servers to choose from. The Web site http://newzbot.com also contains many useful resources. Assuming that your news server is news.foo.bar (this is not a real server name, and won’t work), you can test your NNTP server like this: >>> from nntplib import NNTP >>> server = NNTP('news.foo.bar') >>> server.group('comp.lang.python.announce')[0] ■Note To connect to some servers, you may need to supply additional parameters for authentication. Please consult the Python Library Reference for details on the optional parameters of the NNTP constructor.
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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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x ■CONTENTS ■CHAPTER 5 Conditio
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xxii ■CONTENTS Preparations . . .
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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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110 CHAPTER 6 ■ ABSTRACTION But w
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140 CHAPTER 7 ■ MORE ABSTRACTION
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CHAPTER 9 ■ ■ ■ Magic Methods
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CHAPTER 9 ■ MAGIC METHODS, PROPER
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CHAPTER 10 ■ ■ ■ Batteries In
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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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488 CHAPTER 26 ■ PROJECT 7: YOUR
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500 CHAPTER 27 ■ PROJECT 8: FILE
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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 595 Python C API 365 hand-
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■INDEX 603 further exploration 47
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