最新[Python编程(第4版)].源代码PP4E-Examples-1.4_Python_其他

<html xmlns="http://www.w3.org/1999/xhtml"><head><meta charset="utf-8"><meta name="generator" content="pdf2htmlEX"><meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1"><link rel="stylesheet" href="https://csdnimg.cn/release/download_crawler_static/css/base.min.css"><link rel="stylesheet" href="https://csdnimg.cn/release/download_crawler_static/css/fancy.min.css"><link rel="stylesheet" href="https://csdnimg.cn/release/download_crawler_static/10482660/raw.css"><script src="https://csdnimg.cn/release/download_crawler_static/js/compatibility.min.js"></script><script src="https://csdnimg.cn/release/download_crawler_static/js/pdf2htmlEX.min.js"></script><script>try{pdf2htmlEX.defaultViewer = new pdf2htmlEX.Viewer({});}catch(e){}</script><title></title></head><body><div id="sidebar" style="display: none"><div id="outline"></div></div><div id="pf1" class="pf w0 h0" data-page-no="1"><div class="pc pc1 w0 h0"><img class="bi x0 y0 w1 h1" alt="" src="https://csdnimg.cn/release/download_crawler_static/10482660/bg1.jpg"><div class="t m0 x1 h2 y1 ff1 fs0 fc0 sc0 ls0 ws0">816</div><div class="t m0 x2 h2 y2 ff1 fs0 fc1 sc0 ls0 ws0">This is the Title of the Book, eMatter Edition</div><div class="t m0 x3 h2 y3 ff1 fs0 fc1 sc0 ls0 ws0">Copyright © 2001 O’Reilly & Associates, Inc. All rights reserved.</div><div class="t m0 x4 h3 y4 ff2 fs1 fc1 sc0 ls0 ws0">Chapter 14</div><div class="t m0 x5 h4 y5 ff2 fs2 fc0 sc0 ls1 ws0">14</div><div class="t m0 x1 h5 y6 ff1 fs3 fc0 sc0 ls0 ws0">Larger Web Site</div><div class="t m0 x1 h5 y7 ff1 fs3 fc0 sc0 ls0 ws0">Examples II</div><div class="t m0 x1 h6 y8 ff1 fs4 fc0 sc0 ls0 ws0">“Typos Happen”</div><div class="t m0 x1 h3 y9 ff2 fs1 fc0 sc0 ls0 ws0">This chapter presents the second of two server-side Python web programming</div><div class="t m0 x1 h3 ya ff2 fs1 fc0 sc0 ls0 ws0">case studies. It covers the design and implementation of PyErrata, a CGI-based</div><div class="t m0 x1 h3 yb ff2 fs1 fc0 sc0 ls0 ws0">web site implemented entirely in Python that allows users to post book comments</div><div class="t m0 x1 h3 yc ff2 fs1 fc0 sc0 ls0 ws0">and error reports, and demonstrates the concepts underlying persistent database</div><div class="t m0 x1 h3 yd ff2 fs1 fc0 sc0 ls0 ws0">storage in the CGI world. As we’ll see, this case study teaches both server-side</div><div class="t m0 x1 h3 ye ff2 fs1 fc0 sc0 ls0 ws0">scripting and Python development techniques.</div><div class="t m0 x1 h6 yf ff1 fs4 fc0 sc0 ls0 ws0">The PyErrata Web Site</div><div class="t m0 x1 h3 y10 ff2 fs1 fc0 sc0 ls0 ws0">The last chapter concluded with a discussion of the downsides of deploying appli-</div><div class="t m0 x1 h3 y11 ff2 fs1 fc0 sc0 ls0 ws0">cations on the Web. But now that I’ve told you all the reasons you might not want</div><div class="t m0 x1 h3 y12 ff2 fs1 fc0 sc0 ls0 ws0">to design systems for the Web, I’m going to completely contradict myself and</div><div class="t m0 x1 h3 y13 ff2 fs1 fc0 sc0 ls0 ws0">present a system that cries out for a web-based implementation. This chapter pre-</div><div class="t m0 x1 h3 y14 ff2 fs1 fc0 sc0 ls0 ws0">sents the PyErrata web site, a Python program that lets arbitrary people on arbi-</div><div class="t m0 x1 h3 y15 ff2 fs1 fc0 sc0 ls0 ws0">trary machines submit book comments and bug reports (usually called errata)</div><div class="t m0 x1 h3 y16 ff2 fs1 fc0 sc0 ls0 ws0">over the Web, using just a web browser.</div><div class="t m0 x1 h3 y17 ff2 fs1 fc0 sc0 ls0 ws0">PyErrata is in some ways simpler than the PyMailCgi case study presented in the</div><div class="t m0 x1 h3 y18 ff2 fs1 fc0 sc0 ls0 ws0">previous chapter. From a user’s perspective, PyErrata is more hierarchical than lin-</div><div class="t m0 x1 h3 y19 ff2 fs1 fc0 sc0 ls0 ws0">ear: user interactions are shorter and spawn fewer pages. There is also little state</div><div class="t m0 x1 h3 y1a ff2 fs1 fc0 sc0 ls0 ws0">retention in web pages themselves in PyErrata; URL parameters pass state in only</div><div class="t m0 x1 h3 y1b ff2 fs1 fc0 sc0 ls0 ws0">one isolated case, and no hidden form fields are generated.</div><div class="t m0 x1 h3 y1c ff2 fs1 fc0 sc0 ls0 ws0">On the other hand, PyErrata introduces an entirely new dimension: persistent data</div><div class="t m0 x1 h3 y1d ff3 fs1 fc0 sc0 ls0 ws0">storage. State (error and comment reports) is stored permanently by this system on</div><div class="t m0 x6 h7 y1e ff4 fs5 fc0 sc0 ls0 ws0">,ch14.17404 Page 816 Wednesday, February 7, 2001 2:54 PM</div></div><div class="pi" data-data='{"ctm":[1.568627,0.000000,0.000000,1.568627,0.000000,0.000000]}'></div></div></body></html>

<div id="pf2" class="pf w0 h0" data-page-no="2"><div class="pc pc2 w0 h0"><img class="bi x0 y0 w1 h1" alt="" src="https://csdnimg.cn/release/download_crawler_static/10482660/bg2.jpg"><div class="t m0 x1 h2 y1f ff1 fs0 fc0 sc0 ls0 ws0">The PyErrata Web Site 817</div><div class="t m0 x2 h2 y2 ff1 fs0 fc1 sc0 ls0 ws0">This is the Title of the Book, eMatter Edition</div><div class="t m0 x3 h2 y3 ff1 fs0 fc1 sc0 ls0 ws0">Copyright © 2001 O’Reilly & Associates, Inc. All rights reserved.</div><div class="t m0 x1 h3 y20 ff2 fs1 fc0 sc0 ls0 ws0">the server, either in flat pickle files or a shelve-based database. Both raise the</div><div class="t m0 x1 h3 y21 ff2 fs1 fc0 sc0 ls0 ws0">specter of concurrent updates, since any number of users out in cyberspace may</div><div class="t m0 x1 h3 y22 ff2 fs1 fc0 sc0 ls0 ws0">be accessing the site at the same time.</div><div class="t m0 x1 h8 y23 ff1 fs6 fc0 sc0 ls0 ws0">System Goals</div><div class="t m0 x1 h3 y24 ff2 fs1 fc0 sc0 ls0 ws0">Before you ponder too long over the seeming paradox of a book that comes with</div><div class="t m0 x1 h3 y25 ff2 fs1 fc0 sc0 ls0 ws0">its own bug-reporting system, I should provide a little background. Over the last</div><div class="t m0 x1 h3 y26 ff2 fs1 fc0 sc0 ls0 ws0">five years, I’ve been fortunate enough to have had the opportunity to write four</div><div class="t m0 x1 h3 y27 ff2 fs1 fc0 sc0 ls0 ws0">books, a large chapter in a reference book, and various magazine articles and</div><div class="t m0 x1 h3 y28 ff2 fs1 fc0 sc0 ls0 ws0">training materials. Changes in the Python world have also provided opportunities</div><div class="t m0 x1 h3 y29 ff2 fs1 fc0 sc0 ls0 ws0">to rewrite books from the ground up. It’s been both wildly rewarding and lucra-</div><div class="t m0 x1 h3 y2a ff2 fs1 fc0 sc0 ls0 ws0">tive work (well, rewarding, at least).</div><div class="t m0 x1 h3 y2b ff2 fs1 fc0 sc0 ls0 ws0">But one of the first big lessons one learns upon initiation in the publishing busi-</div><div class="t m0 x1 h3 y2c ff2 fs1 fc0 sc0 ls0 ws0">ness is that typos are a fact of life. Really. No matter how much of a perfectionist</div><div class="t m0 x1 h3 y2d ff2 fs1 fc0 sc0 ls0 ws0">you are, books will have bugs. Furthermore, big books tend to have more bugs</div><div class="t m0 x1 h3 y2e ff2 fs1 fc0 sc0 ls0 ws0">than little books, and in the technical publishing domain, readers are often suffi-</div><div class="t m0 x1 h3 y2f ff2 fs1 fc0 sc0 ls0 ws0">ciently savvy and motivated to send authors email when they find those bugs.</div><div class="t m0 x1 h3 y30 ff2 fs1 fc0 sc0 ls0 ws0">That’s a terrific thing, and helps authors weed out typos in reprints. I always</div><div class="t m0 x1 h3 y31 ff2 fs1 fc0 sc0 ls0 ws0">encourage and appreciate email from readers. But I get lots of email—at times, so</div><div class="t m0 x1 h3 y32 ff2 fs1 fc0 sc0 ls0 ws0">much so that given my schedule, I find it difficult to even reply to every message,</div><div class="t m0 x1 h3 y33 ff2 fs1 fc0 sc0 ls0 ws0">let alone investigate and act on every typo report. I get lots of other email too, and</div><div class="t m0 x1 h3 y34 ff2 fs1 fc0 sc0 ls0 ws0">can miss a reader’s typo report if I’m not careful.</div><div class="t m0 x1 h3 y35 ff2 fs1 fc0 sc0 ls0 ws0">About a year ago, I realized that I just couldn’t keep up with all the traffic and</div><div class="t m0 x1 h3 y36 ff2 fs1 fc0 sc0 ls0 ws0">started thinking about alternatives. One obvious way to cut down on the over-</div><div class="t m0 x1 h3 y37 ff2 fs1 fc0 sc0 ls0 ws0">head of managing reports is to delegate responsibility—to offload at least some</div><div class="t m0 x1 h3 y38 ff2 fs1 fc0 sc0 ls0 ws0">report-processing tasks to the people who generate the reports. That is, I needed</div><div class="t m0 x1 h3 y39 ff2 fs1 fc0 sc0 ls0 ws0">to somehow provide a widely available system, separate from my email account,</div><div class="t m0 x1 h3 y3a ff2 fs1 fc0 sc0 ls0 ws0">that automates report posting and logs reports to be reviewed as time allows.</div><div class="t m0 x1 h3 y3b ff2 fs1 fc0 sc0 ls0 ws0">Of course, that’s exactly the sort of need that the Internet is geared to. By imple-</div><div class="t m0 x1 h3 y3c ff2 fs1 fc0 sc0 ls0 ws0">menting an error-reporting system as a web site, any reader can visit and log</div><div class="t m0 x1 h3 y3d ff2 fs1 fc0 sc0 ls0 ws0">reports from any machine with a browser, whether they have Python installed or</div><div class="t m0 x1 h3 y3e ff2 fs1 fc0 sc0 ls0 ws0">not. Moreover, those reports can be logged in a database at the web site for later</div><div class="t m0 x1 h3 y3f ff2 fs1 fc0 sc0 ls0 ws0">inspection by both author and readers, instead of requiring manual extraction from</div><div class="t m0 x1 h3 y40 ff2 fs1 fc0 sc0 ls0 ws0">incoming email.</div><div class="t m0 x1 h3 y41 ff2 fs1 fc0 sc0 ls0 ws0">The implementation of these ideas is the PyErrata system—a web site imple-</div><div class="t m0 x1 h3 y42 ff2 fs1 fc0 sc0 ls0 ws0">mented with server-side Python programs. PyErrata allows readers to post bug</div><div class="t m0 x1 h3 y43 ff2 fs1 fc0 sc0 ls0 ws0">reports and comments about this edition of Programming Python, as well as view</div><div class="t m0 x1 h3 y44 ff2 fs1 fc0 sc0 ls0 ws0">the collection of all prior posts by various sort keys. Its goal is to replace the tradi-</div><div class="t m0 x1 h3 y45 ff2 fs1 fc0 sc0 ls0 ws0">tional errata list pages I’ve had to maintain manually for other books in the past.</div><div class="t m0 x6 h7 y1e ff4 fs5 fc0 sc0 ls0 ws0">,ch14.17404 Page 817 Wednesday, February 7, 2001 2:54 PM</div></div><div class="pi" data-data='{"ctm":[1.568627,0.000000,0.000000,1.568627,0.000000,0.000000]}'></div></div>

<div id="pf3" class="pf w0 h0" data-page-no="3"><div class="pc pc3 w0 h0"><img class="bi x0 y0 w1 h1" alt="" src="https://csdnimg.cn/release/download_crawler_static/10482660/bg3.jpg"><div class="t m0 x1 h2 y1f ff1 fs0 fc0 sc0 ls0 ws0">818 Chapter 14: Larger Web Site Examples II</div><div class="t m0 x2 h2 y2 ff1 fs0 fc1 sc0 ls0 ws0">This is the Title of the Book, eMatter Edition</div><div class="t m0 x3 h2 y3 ff1 fs0 fc1 sc0 ls0 ws0">Copyright © 2001 O’Reilly & Associates, Inc. All rights reserved.</div><div class="t m0 x1 h3 y20 ff2 fs1 fc0 sc0 ls0 ws0">More than any other web-based example in this book, PyErrata demonstrates just</div><div class="t m0 x1 h3 y21 ff2 fs1 fc0 sc0 ls0 ws0">how much work can be saved with a little Internet scripting. To support the first</div><div class="t m0 x1 h3 y22 ff2 fs1 fc0 sc0 ls0 ws0">edition of this book, I hand-edited an HTML file that listed all known bugs. With</div><div class="t m0 x1 h3 y46 ff2 fs1 fc0 sc0 ls0 ws0">PyErrata, server-side programs generate such pages dynamically from a user-popu-</div><div class="t m0 x1 h3 y47 ff2 fs1 fc0 sc0 ls0 ws0">lated database. Because list pages are produced on demand, PyErrata not only</div><div class="t m0 x1 h3 y48 ff2 fs1 fc0 sc0 ls0 ws0">publishes and automates list creation, it also provides multiple ways to view report</div><div class="t m0 x1 h3 y49 ff2 fs1 fc0 sc0 ls0 ws0">data. I wouldn’t even try to reorder the first edition’s static HTML file list.</div><div class="t m0 x1 h3 y26 ff2 fs1 fc0 sc0 ls0 ws0">PyErrata is something of an experiment in open systems, and as such is vulnera-</div><div class="t m0 x1 h3 y27 ff2 fs1 fc0 sc0 ls0 ws0">ble to abuse. I still have to manually investigate reports, as time allows. But it at</div><div class="t m0 x1 h3 y28 ff2 fs1 fc0 sc0 ls0 ws0">least has the potential to ease one of the chores that generally goes unmentioned</div><div class="t m0 x1 h3 y29 ff2 fs1 fc0 sc0 ls0 ws0">in typical publishing contracts.</div><div class="t m0 x1 h8 y4a ff1 fs6 fc0 sc0 ls0 ws0">Implementation Overview</div><div class="t m0 x1 h3 y4b ff2 fs1 fc0 sc0 ls0 ws0">Like other web-based systems in this part of the book, PyErrata consists of a col-</div><div class="t m0 x1 h3 y4c ff2 fs1 fc0 sc0 ls0 ws0">lection of HTML files, Python utility modules, and Python-coded CGI scripts that</div><div class="t m0 x1 h3 y4d ff2 fs1 fc0 sc0 ls0 ws0">run on a shared server instead of on a client. Unlike those other web systems,</div><div class="t m0 x1 h3 y4e ff2 fs1 fc0 sc0 ls0 ws0">PyErrata also implements a persistent database and defines additional directory</div><div class="t m0 x1 h3 y4f ff2 fs1 fc0 sc0 ls0 ws0">structures to support it. Figure 14-1 shows the top-level contents of the site, seen</div><div class="t m0 x1 h3 y50 ff2 fs1 fc0 sc0 ls0 ws0">on Windows from a PyEdit Open dialog.</div><div class="t m0 x1 h3 y51 ff2 fs1 fc0 sc0 ls0 ws0">You will find a similar structure on this book’s CD-ROM. To install this site on the</div><div class="t m0 x1 h3 y52 ff2 fs1 fc0 sc0 ls0 ws0">Net, all the files and directories you see here are uploaded to the server machine</div><div class="t m0 x1 h3 y53 ff2 fs1 fc0 sc0 ls0 ws0">and stored in a PyErrata subdirectory within the root of the directory that is</div><div class="t m0 x1 h9 y54 ff3 fs0 fc0 sc0 ls0 ws0">Figure 14-1. PyErrata site contents</div><div class="t m0 x6 h7 y1e ff4 fs5 fc0 sc0 ls0 ws0">,ch14.17404 Page 818 Wednesday, February 7, 2001 2:54 PM</div></div><div class="pi" data-data='{"ctm":[1.568627,0.000000,0.000000,1.568627,0.000000,0.000000]}'></div></div>

<div id="pf4" class="pf w0 h0" data-page-no="4"><div class="pc pc4 w0 h0"><img class="bi x0 y0 w1 h1" alt="" src="https://csdnimg.cn/release/download_crawler_static/10482660/bg4.jpg"><div class="t m0 x1 h2 y1f ff1 fs0 fc0 sc0 ls0 ws0">The PyErrata Web Site 819</div><div class="t m0 x2 h2 y2 ff1 fs0 fc1 sc0 ls0 ws0">This is the Title of the Book, eMatter Edition</div><div class="t m0 x3 h2 y3 ff1 fs0 fc1 sc0 ls0 ws0">Copyright © 2001 O’Reilly & Associates, Inc. All rights reserved.</div><div class="t m0 x1 h3 y20 ff2 fs1 fc0 sc0 ls0 ws0">exposed to the Web (my public_html directory). The top-level files of this site</div><div class="t m0 x1 h3 y21 ff2 fs1 fc0 sc0 ls0 ws0">implement browse and submit operations as well as database interfaces. A few</div><div class="t m0 x1 h3 y22 ff2 fs1 fc0 sc0 ls0 ws0">resource page files and images show up in this listing too, but are ignored in this</div><div class="t m0 x1 h3 y46 ff2 fs1 fc0 sc0 ls0 ws0">book. Besides files, this site has subdirectories of its own:</div><div class="t m0 x1 h3 y55 ff2 fs1 fc0 sc0 ls0 ws0">• Mutex is a Python package that contains a mutual-exclusion utility module</div><div class="t m0 x7 h3 y24 ff2 fs1 fc0 sc0 ls0 ws0">used for shelves, as well as test scripts for this utility model.</div><div class="t m0 x1 h3 y56 ff2 fs1 fc0 sc0 ls0 ws0">• AdminTools includes system utility scripts that are run standalone from the</div><div class="t m0 x7 h3 y57 ff2 fs1 fc0 sc0 ls0 ws0">command line.</div><div class="t m0 x1 h3 y58 ff2 fs1 fc0 sc0 ls0 ws0">• DbaseFiles holds the file-based database, with separate subdirectories for</div><div class="t m0 x7 h3 y59 ff2 fs1 fc0 sc0 ls0 ws0">errata and comment pickle files.</div><div class="t m0 x1 h3 y5a ff2 fs1 fc0 sc0 ls0 ws0">• DbaseShelve contains the shelve-based database, with separate shelve files for</div><div class="t m0 x7 h3 y5b ff2 fs1 fc0 sc0 ls0 ws0">errata and comments.</div><div class="t m0 x1 h3 y2c ff2 fs1 fc0 sc0 ls0 ws0">We’ll meet the contents of the database subdirectories later in this chapter, when</div><div class="t m0 x1 h3 y2d ff2 fs1 fc0 sc0 ls0 ws0">exploring the database implementation.</div><div class="t m0 x1 h8 y5c ff1 fs6 fc0 sc0 ls0 ws0">Presentation Strategy</div><div class="t m0 x1 h3 y5d ff2 fs1 fc0 sc0 ls0 ws0">PyErrata takes logic factoring, code reuse, and encapsulation to extremes. Top-</div><div class="t m0 x1 h3 y5e ff2 fs1 fc0 sc0 ls0 ws0">level scripts, for example, are often just a few lines long and ultimately invoke</div><div class="t m0 x1 h3 y5f ff2 fs1 fc0 sc0 ls0 ws0">generic logic in common utility modules. With such an architecture, mixing short</div><div class="t m0 x1 h3 y60 ff2 fs1 fc0 sc0 ls0 ws0">code segments with lots of screen shots makes it tough to trace the flow of con-</div><div class="t m0 x1 h3 y61 ff2 fs1 fc0 sc0 ls0 ws0">trol through the program.</div><div class="t m0 x1 h3 y62 ff2 fs1 fc0 sc0 ls0 ws0">To make this system easier to study, we’re going to take a slightly different</div><div class="t m0 x1 h3 y63 ff2 fs1 fc0 sc0 ls0 ws0">approach here. PyErrata’s implementation will be presented in three main sections</div><div class="t m0 x1 h3 y64 ff2 fs1 fc0 sc0 ls0 ws0">corresponding to major functional areas of the system: report browsing, report</div><div class="t m0 x1 h3 y65 ff2 fs1 fc0 sc0 ls0 ws0">submission, and database interfaces. The site root page will be shown before these</div><div class="t m0 x1 h3 y66 ff2 fs1 fc0 sc0 ls0 ws0">three sections, but mostly just for context; it’s simple, static HTML.</div><div class="t m0 x1 h3 y67 ff2 fs1 fc0 sc0 ls0 ws0">Within the browsing and submission sections, all user interaction models (and</div><div class="t m0 x1 h3 y68 ff2 fs1 fc0 sc0 ls0 ws0">screen shots) are shown first, followed by all the source code used to implement</div><div class="t m0 x1 h3 y69 ff2 fs1 fc0 sc0 ls0 ws0">that interaction. Like the PyForm example in Chapter 16, Databases and Persis-</div><div class="t m0 x1 h3 y6a ff3 fs1 fc0 sc0 ls0 ws0">tence, PyErrata is at heart a database-access program, and its database interfaces</div><div class="t m0 x1 h3 y6b ff2 fs1 fc0 sc0 ls0 ws0">are ultimately the core of the system. Because these interfaces encapsulate most</div><div class="t m0 x1 h3 y6c ff2 fs1 fc0 sc0 ls0 ws0">low-level storage details, though, we’ll save their presentation for last.</div><div class="t m0 x1 h3 y6d ff2 fs1 fc0 sc0 ls0 ws0">Although you still may have to jump around some to locate modules across func-</div><div class="t m0 x1 h3 y6e ff2 fs1 fc0 sc0 ls0 ws0">tional boundaries, this organization of all the code for major chunks of the system</div><div class="t m0 x1 h3 y6f ff2 fs1 fc0 sc0 ls0 ws0">in their own sections should help minimize page-flipping.</div><div class="t m0 x6 h7 y1e ff4 fs5 fc0 sc0 ls0 ws0">,ch14.17404 Page 819 Wednesday, February 7, 2001 2:54 PM</div></div><div class="pi" data-data='{"ctm":[1.568627,0.000000,0.000000,1.568627,0.000000,0.000000]}'></div></div>

<div id="pf5" class="pf w0 h0" data-page-no="5"><div class="pc pc5 w0 h0"><img class="bi x0 y0 w1 h1" alt="" src="https://csdnimg.cn/release/download_crawler_static/10482660/bg5.jpg"><div class="t m0 x1 h2 y1f ff1 fs0 fc0 sc0 ls0 ws0">820 Chapter 14: Larger Web Site Examples II</div><div class="t m0 x2 h2 y2 ff1 fs0 fc1 sc0 ls0 ws0">This is the Title of the Book, eMatter Edition</div><div class="t m0 x3 h2 y3 ff1 fs0 fc1 sc0 ls0 ws0">Copyright © 2001 O’Reilly & Associates, Inc. All rights reserved.</div><div class="t m0 x1 h6 y70 ff1 fs4 fc0 sc0 ls0 ws0">The Root Page</div><div class="t m0 x1 h3 y71 ff2 fs1 fc0 sc0 ls0 ws0">Let’s start at the top. In this chapter we will study the complete implementation of</div><div class="t m0 x1 h3 y72 ff2 fs1 fc0 sc0 ls0 ws0">PyErrata, but readers are also encouraged to visit the web site where it lives to</div><div class="t m0 x1 h3 y73 ff2 fs1 fc0 sc0 ls0 ws0">sample the flavor of its interaction first-hand. Unlike PyMailCgi, there are no pass-</div><div class="t m0 x1 h3 y74 ff2 fs1 fc0 sc0 ls0 ws0">word constraints in PyErrata, so you can access all of its pages without any config-</div><div class="t m0 x1 h3 y75 ff2 fs1 fc0 sc0 ls0 ws0">uration steps.</div><div class="t m0 x1 h3 y76 ff2 fs1 fc0 sc0 ls0 ws0">PyErrata installs as a set of HTML files and Python CGI scripts, along with a few</div><div class="t m0 x1 h3 y77 ff2 fs1 fc0 sc0 ls0 ws0">image files. As usual, you can simply point your web browser to the system’s root</div><div class="t m0 x1 h3 y78 ff2 fs1 fc0 sc0 ls0 ws0">page to run the system live while you study this chapter. Its root page currently</div><div class="t m0 x1 h3 y79 ff2 fs1 fc0 sc0 ls0 ws0">lives here:</div><div class="t m0 x8 ha y3d ff2 fs7 fc0 sc0 ls0 ws0">*</div><div class="t m0 x7 hb y7a ff3 fs1 fc0 sc0 ls0 ws0">http://starship.python.net/~lutz/PyErrata/pyerrata.html</div><div class="t m0 x1 h3 y7b ff2 fs1 fc0 sc0 ls0 ws0">If you go to this address, your browser will be served the page shown in</div><div class="t m0 x1 h3 y7c ff2 fs1 fc0 sc0 ls0 ws0">Figure 14-2. PyErrata supports both submission and browsing of comments and</div><div class="t m0 x9 h8 y7d ff1 fs6 fc0 sc0 ls0 ws0">Use the Source, Luke</div><div class="t m0 xa h3 y7e ff2 fs1 fc0 sc0 ls0 ws0">I want to insert the standard case-study caveat here: although this chapter does</div><div class="t m0 xa h3 y7f ff2 fs1 fc0 sc0 ls0 ws0">explain major concepts along the way, understanding the whole story is left</div><div class="t m0 xa h3 y80 ff2 fs1 fc0 sc0 ls0 ws0">partly up to you. As always, please consult the source code listings in this chap-</div><div class="t m0 xa h3 y81 ff2 fs1 fc0 sc0 ls0 ws0">ter (and on the CD) for details not spelled out explicitly. I’ve taken this minimal</div><div class="t m0 xa h3 y82 ff2 fs1 fc0 sc0 ls0 ws0">approach deliberately, mostly because I assume you already know a lot about</div><div class="t m0 xa h3 y83 ff2 fs1 fc0 sc0 ls0 ws0">CGI scripting and the Python language by this point in the book, but also</div><div class="t m0 xa h3 y84 ff2 fs1 fc0 sc0 ls0 ws0">because real-world development time is spent as much on reading other peo-</div><div class="t m0 xa h3 y85 ff2 fs1 fc0 sc0 ls0 ws0">ple’s code as on writing your own. Python makes both tasks relatively easy,</div><div class="t m0 xa h3 y86 ff2 fs1 fc0 sc0 ls0 ws0">but now is your chance to see how for yourself.</div><div class="t m0 xa h3 y87 ff2 fs1 fc0 sc0 ls0 ws0">I also wish to confess right off that this chapter has a hidden agenda. PyErrata</div><div class="t m0 xa h3 y88 ff2 fs1 fc0 sc0 ls0 ws0">not only shows more server-side scripting techniques, but also illustrates com-</div><div class="t m0 xa h3 y89 ff2 fs1 fc0 sc0 ls0 ws0">mon Python development concepts at large. Along the way, we focus on this</div><div class="t m0 xa h3 y8a ff2 fs1 fc0 sc0 ls0 ws0">system’s current software architecture and point out a variety of design alter-</div><div class="t m0 xa h3 y8b ff2 fs1 fc0 sc0 ls0 ws0">natives. Be sure to pay special attention to the way that logic has been layered</div><div class="t m0 xa h3 y2e ff2 fs1 fc0 sc0 ls0 ws0">into multiple abstraction levels. For example, by separating database and user-</div><div class="t m0 xa h3 y8c ff2 fs1 fc0 sc0 ls0 ws0">interface (page generation) code, we minimize code redundancy and cross-</div><div class="t m0 xa h3 y8d ff2 fs1 fc0 sc0 ls0 ws0">module dependencies and maximize code reuse. Such techniques are useful</div><div class="t m0 xa h3 y8e ff2 fs1 fc0 sc0 ls0 ws0">in all Python systems, web-based or not.</div><div class="t m0 x1 ha y8f ff2 fs7 fc0 sc0 ls0 ws0">* But be sure to see this book’s web site, http://rmi.net/~lutz/about-pp.html, for an updated link if the</div><div class="t m0 xb ha y90 ff2 fs7 fc0 sc0 ls0 ws0">one listed here no longer works by the time you read this book. Web sites seem to change addresses</div><div class="t m0 xb ha y91 ff2 fs7 fc0 sc0 ls0 ws0">faster than developers change jobs.</div><div class="t m0 x6 h7 y1e ff4 fs5 fc0 sc0 ls0 ws0">,ch14.17404 Page 820 Wednesday, February 7, 2001 2:54 PM</div></div><div class="pi" data-data='{"ctm":[1.568627,0.000000,0.000000,1.568627,0.000000,0.000000]}'></div></div>