CS1116/CS5018
Web Development 2
Dr Derek Bridge
School of Computer Science & Information Technology
University College Cork
Case study 1A: a Web page comments facility
- Suppose you have a Web page,
page.html
- Suppose you want to allow visitors to the page to
- view the comments that have been posted
What we will do
- We will create a database where we can store the comments
- We will replace the Web page (
page.html)
by a server-side Python program (page.py)
- It will be a self-processing page
- Its form will use the HTTP post method, not the get method
Q: Why?
MySQL database for the Web page comments facility
CREATE TABLE comments_table
(
comment_id INT AUTO_INCREMENT,
username VARCHAR(255),
comment TEXT,
PRIMARY KEY (comment_id)
);
The Web page/Python program, page.py
#!/usr/local/bin/python3
from cgitb import enable
enable()
from cgi import FieldStorage
import pymysql as db
print('Content-Type: text/html')
print()
comments = ''
try:
connection = db.connect('localhost', 'userid', 'password', 'database_name')
cursor = connection.cursor(db.cursors.DictCursor)
form_data = FieldStorage()
if len(form_data) != 0:
username = form_data.getfirst('username')
new_comment = form_data.getfirst('new_comment')
cursor.execute("""INSERT INTO comments_table (username, comment)
VALUES (%s, %s)""", (username, new_comment))
connection.commit()
cursor.execute("""SELECT * FROM comments_table
ORDER BY comment_id DESC""")
for row in cursor.fetchall():
comments += '<article><h1>%s</h1><p>%s</p></article>' % (row['username'], row['comment'])
cursor.close()
connection.close()
except db.Error:
comments = '<p>Sorry! We are experiencing problems at the moment. Please call back later.</p>'
print("""
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8" />
<title>My Web Page</title>
</head>
<body>
<p>
Hello! This is my Web page!
</p>
<section>
<h1>Comments</h1>
<form action="page.py" method="post">
<fieldset>
<legend>Post a new comment</legend>
<label for="username">Name:</label>
<input type="text" name="username" id="username" />
<label for="new_comment">Comment:</label>
<textarea name="new_comment" id="new_comment" rows="5" cols="50">
</textarea>
<input type="submit" />
</fieldset>
</form>
%s
</section>
</body>
</html>""" % (comments))
Case study 1B: a Web site comments facility
- Suppose you have a Web site with lots of pages (e.g.
page1.html, page2.html, etc.)
- Suppose you want to allow visitors to
- post comments on more than one page in a Web site
- view the comments that have been posted
What we will do
- We will create a slightly different database
- We will write a separate Python module,
comments.py
- We will replace every Web page (
page1.html,
page2.html) by server-side Python programs
(page1.py, page2.py, etc.)
- We will use
import to load in our new module
MySQL database for the Web site comments facility
CREATE TABLE comments_table
(
comment_id INT AUTO_INCREMENT,
username VARCHAR(255),
url VARCHAR(255) NOT NULL,
comment TEXT,
PRIMARY KEY (comment_id)
);
A typical Web page/Python program, page1.py
#!/usr/local/bin/python3
from cgitb import enable
enable()
from comments import get_comments
print('Content-Type: text/html')
print()
print("""
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8" />
<title>One Of My Web Pages</title>
</head>
<body>
<p>
Hello! This is one of my Web pages!
</p>
%s
</body>
</html>""" % (get_comments()))
The new module, comments.py
#!/usr/local/bin/python3
from cgitb import enable
enable()
def get_comments():
from cgi import FieldStorage
import pymysql as db
from os import environ
comments = ''
url = environ.get('SCRIPT_NAME')
try:
connection = db.connect('localhost', 'userid', 'password', 'database_name')
cursor = connection.cursor(db.cursors.DictCursor)
form_data = FieldStorage()
if len(form_data) != 0:
username = form_data.getfirst('username')
new_comment = form_data.getfirst('new_comment')
cursor.execute("""INSERT INTO comments_table (username, url, comment)
VALUES (%s, %s, %s)""", (username, url, new_comment))
connection.commit()
cursor.execute("""SELECT * FROM comments_table
WHERE url = %s
ORDER BY comment_id DESC""", (url))
for row in cursor.fetchall():
comments += '<article><h1>%s</h1><p>%s</p></article>' % (row['username'], row['comment'])
cursor.close()
connection.close()
except db.Error:
comments = '<p>Sorry! We are experiencing problems at the moment. Please call back later.</p>'
return """
<section>
<h1>Comments</h1>
<form action="%s" method="post">
<fieldset>
<legend>Post a new comment</legend>
<label for="username">Name:</label>
<input type="text" name="username" id="username" />
<label for="new_comment">Comment:</label>
<textarea name="new_comment" id="new_comment" rows="5" cols="50">
</textarea>
<input type="submit" />
</fieldset>
</form>
%s""" % (url, comments)