Beginning Python - From Novice to Professional

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CHAPTER 25 ■ ■ ■ Project 6: Remote Editing with CGI This project uses CGI, which is discussed in more detail in Chapter 15. The specific application is remote editing—editing a document on another machine via the Web. This can be useful in collaboration systems (groupware), for example, where several people may be working on the same document. It can also be useful for updating your Web pages. What’s the Problem? The problem is quite simple: You have a document stored on one machine and want to be able to edit it from another machine via the Web. This enables you to have a shared document edited by several collaborating authors—you won’t need to use FTP or similar file transfer technologies, and you won’t need to worry about synchronizing multiple copies. To edit the file, all you need is a browser. ■Note This sort of remote editing is one of the core mechanisms of wikis (see, for example, http:// en.wikipedia.org/wiki/Wiki). Specific Goals The system should be able to do the following: • Display the document as a normal Web page. • Display the document in a text area in a Web form. • Let you save the text from the form. • Protect the document with a password. • Be easily extensible to more than one document. 473
474 CHAPTER 25 ■ PROJECT 6: REMOTE EDITING WITH CGI As you’ll see, all of this is quite easy to do with the standard Python library module cgi and some plain Python coding. However, the techniques used in this application can be used for creating Web interfaces to all of your Python programs—pretty useful. (For example, you use the same CGI techniques in Chapter 15.) Useful Tools The main tool when writing CGI programs is, as discussed in Chapter 15, the cgi module, along with the cgitb module for debugging. See Chapter 15 for more information. Preparations The steps needed for making your CGI script accessible through the Web are described in detail in Chapter 15 in the section “Dynamic Web Pages with CGI.” Just follow those steps, and you should be fine. First Implementation The first implementation is based on the basic structure of the greeting script shown in Listing 15-7 (Chapter 15). All that’s needed for the first prototype is some file handling... For the script to be useful, it must store the edited text between invocations. Also, the form should be made a bit bigger than in the greeting script (simple3.cgi from Listing 15-7 in Chapter 15) and the text field should be changed into a text area. You should also use the POST CGI method instead of the default GET method. (Using POST is normally the thing to do if you are submitting large amounts of data.) The general logic of the program is as follows: 1. Get the CGI parameter text with the current value of the data file as the default. 2. Save the text to the data file. 3. Print out the form, with the text in the textarea. In order for the script to be allowed to write to your data file, you must first create such a file (for example, simple_edit.dat). It can be empty or perhaps contain the initial document (a plain text file, possibly containing some form of markup such as XML or HTML). Then you must set the permissions so that it is universally writable, as described in Chapter 15. The resulting code is shown in Listing 25-1. Listing 25-1. A Simple Web Editor (simple_edit.cgi) #!/usr/bin/env python import cgi form = cgi.FieldStorage()
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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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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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524 CHAPTER 28 ■ PROJECT 9: FILE
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572 APPENDIX C ■ ONLINE RESOURCES
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Index ■Symbols - operator 558 !=
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