Using Python to Query MySQL over the Net

Mihai shows how Python can be used to create a CGI script to enable elegant searching.
The HTML Form

The user should be able to search the database for several items like the tournament name, the black and white player names, the date of the game (at least the year) and also the winner of the game. All this information is available in the SGF files along with the actual game record.

So, I wrote the HTML document shown in Listing 1. Yes, I like to write HTML by hand, and there is no need for anything more complicated. Of course, “myhost” has to be replaced with the actual hostname of the web server. The reader will also notice the HTML form acts by calling the CGI script named search.py once the submit button is clicked. The appearance of the document loaded by Netscape is shown in Figure 3.

Listing 1. Archive Search

Figure 3. Document as Loaded in Netscape

The Igo Database

Each item in the HTML form has to be described in the database. To this end, I created a new database to store the tables. This is done as root, by typing:

myhost:~# mysqladmin create igo

where igo is the new database name. This is not enough though, because only root will have access to the new database. To grant only SELECT privileges to all users for the new database, root has to type:

myhost:~# mysql mysql
mysql> insert into db values (
'%','igo','','Y','N', 'N', 'N', 'N','N','N', 'N',
     'N', 'N');
This changes the table database in the MySQL internal database by adding an entry for the igo database. Then, the MySQL dæmon has to be restarted or the command mysql> flush privileges; has to be typed so that the MySQL dæmon becomes aware of the privilege change.

Now all users should be able to access data in database igo, but only root can change the data.

The MySQL Tables

Creating the tables (one for each tournament) was easy. For instance, a table named gosei, for the tournament Gosei, was made with the following commands:

myhost:~# mysql igo
mysql> create table gosei (
        black varchar(30),
        white varchar(30),
        dt date,
        rez varchar(30),
        fname varchar(30),
        ;
Query OK, 0 rows affected, (0.00 sec)
mysql>

The table has five columns: black player's name, white player's name, the date of the game, the result and finally, the corresponding SGF file name.

Loading the data in the table is another matter. I suppose one way would be to type:

mysql> insert into gosei values ('Cho Chikun', 'Kato Masao', '1987-07-03', 'B+3.5', 'gosei87_1.sgf' );

but I'd rather learn a new programming language than enter that a thousand times. Fortunately, there is another way of loading data in a MySQL table—from a text file. Each row in the file matches a row in the table, and the fields are separated by white spaces, as shown in Table 1.

Table 1. Text to Be Loaded to MySQL Table

Suppose this file is also named gosei. To pass the data to a MySQL table, one would write

mysql> load data infile "gosei" into table gosei;

Then a query result should look like Table 2.

Table 2. Loading from a Text File

The reader might ask “Okay, but isn't making a huge text file another burden?” Actually, that's an easy task for yet another small Python script (that I will not show, because it's not directly related to our topic).

With the igo database created and the tables loaded with data, there was only one thing left to be done: write the Python CGI script that would take input from the user via the HTML form, query the database and produce a list of matching game files.

The Python CGI Script

This program, named search.py is presented in Listing 2 [at the LJ ftp site]. It makes use of two great modules imported in the third and fourth lines. The CGI module is almost like magic: it just gets the data submitted by the HTML form as a Python dictionary. The programmer does not need to be concerned with details like the method (GET or POST) used to send form data to the CGI script. Don't you love Python?

The MySQL module is also easy to use. With four simple statements, it opens the connection to the desired database, sends the query, gets the results and stores them in a list of row lists (a Python list whose members each contain one row).

The script has the following structure: getting the HTML form data, creating the database query string according to the form data and querying a table and printing the matching results.

Since there is one for each Go tournament, step three is repeated through a for loop as many times as necessary. The Python code and the appended comments are rather self-explanatory, so I will only comment on the lines:

print '<li><a href="http://myhost' + \
'/cgi-bin/getsgf.py?file=' + e[0] + '">'
print e[0] + '</a>'

Here, e[0] is an SGF file name. Instead of merely printing the filename (which would be of limited help to the user), the print statements create an HTML anchor that sends the filename to the CGI script getsgf.py. This last script (which for the sake of simplicity will not be shown here) searches for the actual path to the SGF file and starts a Java applet to display the contents of the file in a nice, graphical way.

Of course, both search.py and getsgf.py must be made executable and moved to the cgi-bin directory. Also, a final trap to avoid: all the SGF game files must be placed somewhere within the DocumentRoot directory (as defined in httpd configuration files) in order to be found by a CGI script.

The result of running search.py is displayed in Figure 4 as seen by the user. Clicking on each filename starts the applet shown in Figure 5, which gradually displays the moves of the game.

Figure 4. search.py Results

Figure 5. gose:80_3.sgf Applet

______________________

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Python CGI script -> MySQL database tables retrieving

Sampath Girish's picture

Hi Mihai Bisca,
This is sampath. I am trying to retrieve tables from database usng Python CGI scripts and MySQL as backend. I am able to display an empty web page and unable to get the tables from database.
Its not displaying a line 'Hi' which i kept after

import MySQLdb
import cgi, Cookie

print 'HI'

I ran this along with script for retrieving tables in database in IDLE. It ran successfully. But now its unable to display in web browser. How can i do that?

please send me the reply to my email id if possible. Its girishmsampath@gmail.com

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