Python Tutorial: A Tutorial

Creating dynamic websites with Python with mod_python and WSGI

Introduction

Please notice:
Work on this topic is under process. (August 2014)


mod_python is an Apache HTTP Server module. It's purpose is to integrate Python programming with the Apache web server, or in other words a Python language binding for the Apache HTTP Server. The official website of mod_python says that it possible to write "with mod_python web-based applications in Python that run many times faster than traditional CGI and will have access to advanced features such as ability to retain database connections and other data between hits and access to Apache internals." mod_python has been pronounced dead some years ago. So it didn't look to be a good idea to use it for new projects. It never died, it was only "sleeping". It came to life again in 2013!

Python and mod_python

If we want to use Python on am Apache web server, we need the mod_python module for Apache. This module provides a Python language binding so that we can integrate Python. It's a more efficient approach than using CGI, because CGI will start a new Python process for every request.

Mod_python consists of two components: The dynamically loadable module mod_python.so for Apache and the Python package mod_python. If you are using Debian or Ubuntu Linux, it's satisfying to install the package libapache2-mod-python for this purpose, assuming apache2 is already installed:
sudo apt-get install libapache2-mod-python
If apache2 has to be installed as well, do the following installation first:
sudo apt-get install apache2
You have to add the following lines into /etc/apache2/sites-enabled/000-default:

   AddHandler mod_python .py
 	PythonHandler mod_python.publisher
 	PythonDebug On
It may look like this: ServerAdmin webmaster@localhost DocumentRoot /var/www/html AddHandler mod_python .py PythonHandler mod_python.publisher PythonDebug On Now we have to restart the Apache server:
sudo /etc/init.d/apache2 restart

A Simple Dynamic Page with mod_python

We will create a subdirectory "tests" in the documents root of the Apache server. In case of Debian and Ubuntu, this will be /var/www/html/. We save the following Python program as "hello.py" in the previously created subdirectory:
def index():
    return "Hello Python!"
We have to start a browser and go to the location "localhost/tests/hello.py/index". It works with "localhost/tests/hello.py" as well. We get the following output in the browser window:

Hello Python, View in Browser

Another more "Useful" webpage

We save the following website as timesite.py. It will print out the current date and time, as well as the timezone:
import time
def index():
        html = """
<html><head>
<title>mod_python.publisher first html page</title>
</head>
<body>
<h1>This page was generated by mod_python.publisher</h1><hr>
The local time of this server is:  %s
<br>The timezone of this server is  :  %s
</body>
</html>
""" % (time.ctime(time.time()), time.timezone/3600)
        return html
</pre>


We get the following output:

Time and Date plus Time Zone website

Another Page Name

So far we used index as the default website name. We can also define other functions and by doing so create websites with other names. We write the get_time function in following example and modify the index function:

import time
def index():
        return "index().. nothing here, but you will find some info at get_time .."
def get_time():
        html = """
<html><head>
<title>get_time function</title>
</head>
<body>
<h1>get_time function</h1>
<hr>
The local time of this server is:  %s <br>
The timezone of this server is  :  %s <br>
</body>
</html>""" % (time.ctime(time.time()), time.timezone/3600)
        return html



Calling the location "http://localhost/tests/timesite2.py/get_time", returns the following output:

Time and Date plus Time Zone website

Using the address "http://localhost/tests/timesite2.py/index", supplies this:

Time and Date plus Time Zone website

Using Forms

HTML forms are used to pass data to a server. We can do this with mod_python as well. The following html form inside our Python program "form.py" contains fields for the first name, last name email address and radio buttons for the gender:

def index():

	return """
<html><head>
<title>Formular</title>
</head>
<body>
<FORM value="form" action="get_info" method="post">
  <P>
	<LABEL for="firstname">First Name: </LABEL>
	<INPUT type="text" name="firstname"><BR>
	<LABEL for="lastname">Last Name: </LABEL>
	<INPUT type="text" name="lastname"><BR>
	<LABEL for="email">email: </LABEL>
	<INPUT type="text" name="email"><BR>
	<INPUT type="radio" name="gender" value="Male">Male<BR>
	<INPUT type="radio" name="gender" value="Female">Female<BR>
	<INPUT type="submit" value="Send"> <INPUT type="reset">
  </P>
</FORM>
</body>
</html>
"""

def get_info(req):
	info = req.form
	first = info['firstname']
	last = info['lastname']
	email = info['email']
	gender = info['gender']
	return """
<html><head>
<title>POST method using mod_python</title>
</head>
<body>
<h1>POST Method using mod_python</h1>
<hr>
Thanks for using our service:<br>
Your first name: %s <br>
Your last name: %s <br>
Your email address: %s <br>
Your gender: %s <br>
</body>
</html>
""" %(first, last.upper(), email, gender.lower())

Calling the above program with the URL "http://localhost/tests/form.py/index" gives us the following entry form:

Form for filling in data

To see the result page, i.e. the result of the function get_info, we have to push the "send" button:

Receiving Data from form

WSGI

What is WSGI?

WSGI is the Web Server Gateway Interface. It is a specification that describes how web servers communicate with web applications. It is a framework for the Python. It was originally specified in 2003. WSGI has become a standard for Python web application development. WSGI has been specified in PEP 3333. The abstract says "This document specifies a proposed standard interface between web servers and Python web applications or frameworks, to promote web application portability across a variety of web servers."