Beginning Python - From Novice to Professional

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CHAPTER 26 ■ PROJECT 7: YOUR OWN BULLETIN BOARD 489 curs.execute('SELECT * FROM messages') rows = curs.dictfetchall() toplevel = [] children = {} for row in rows: parent_id = row['reply_to'] if parent_id is None: toplevel.append(row) else: children.setdefault(parent_id,[]).append(row) def format(row): print row['subject'] try: kids = children[row['id']] except KeyError: pass else: print '' for kid in kids: format(kid) print '' print '' for row in toplevel: format(row) print """ """ ■Tip If, for some reason, you can’t get the program to work, it may be that you haven’t set up your database properly. You should consult the documentation for your database to see what is needed in order to let a given user connect and to modify the database. You may, for example, have to list the IP address of the connecting machine explicitly. Second Implementation The first implementation was quite limited in that it didn’t even allow users to post messages. In this section, you expand on the simple system in the first prototype, which contains the
490 CHAPTER 26 ■ PROJECT 7: YOUR OWN BULLETIN BOARD basic structure for the final version. Some measures will be added to check the supplied parameters (such as checking whether reply_to is really a number, and whether the required parameters are really supplied), but you should note that making a system like this robust and user-friendly is a tough task. If you intend to use the system (or, I hope, an improved version of your own), you should be prepared to work quite a bit on these issues. But before you can even think of improving stability, you need something that works, right? So—where do you begin? How do you structure the system? A simple way of structuring Web programs (using technologies such as CGI) is to have one script per action performed by the user. In the case of this system, that would mean the following scripts: main.cgi: Displays the subjects of all messages (threaded) with links to the articles themselves. view.cgi: Displays a single article, and contains a link that will let you reply to it. edit.cgi: Displays a single article in editable form (with text fields and text areas, just like in Chapter 25). Its Submit button is linked to the save script. save.cgi: Receives information about an article (from edit.cgi) and saves it by inserting a new row into the database table. Let’s deal with these separately. main.cgi This script is very similar to the simple_main.cgi script from the first prototype. The main difference is the addition of links. Each subject will be a link to a given message (to view.cgi), and at the bottom of the page you’ll add a link that allows the user to post a new message (a link to edit.cgi). Take a look at the code in Listing 26-4. The line containing the link to each article (part of the format function) looks like this: print '%(subject)s' % row Basically, it creates a link to view.cgi?id=someid where someid is the id of the given row. This syntax (the question mark and key=val) is simply a way of passing parameters to a CGI script—that means if someone clicks this link, they are taken to view.cgi with the id parameter properly set. The “Post message” link is just a link to edit.cgi. So, let’s see how view.cgi handles the id parameter. Listing 26-4. The Main Bulletin Board (main.cgi) #!/usr/bin/python print 'Content-type: text/html\n' import cgitb; cgitb.enable() import psycopg conn = psycopg.connect('dbname=foo user=bar')
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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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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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140 CHAPTER 7 ■ MORE ABSTRACTION
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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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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 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 587 initialization 38 nami
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■INDEX 589 localtime function tim
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■INDEX 591 nesting blocks 88 Netw
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■INDEX 593 playful programming 38
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■INDEX 595 Python C API 365 hand-
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■INDEX 601 TestCase class methods
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