Python and Apache on the Raspberry Pi using the Flask Framework
From reading the Raspberry Pi forum, I see many are wanting to control their hardware projects from the web. Here I will show a method of integrating Python with the Apache web server, and allowing the Apache server access to the GPIO and UART ports without having to run it as root, if you have PHP already installed, both will run in the same environment. For this I am using am using Debian from here: http://www.raspberrypi.org/archives/1435, on a freshly installed SD card.
Part One: Installation, configuration and testing
As root, install the following packages:
# apt-get update
# apt-get upgrade
# apt-get install apache2 libapache2-mod-wsgi python-setuptools python-flask
edit your virtual host in /etc/apache2/sites-enabled, here I have added the wsgi components to the default host 000-default.
Parts easily missed are setting ExecCGI on the Options and adding index.py to the DirectoryIndex. Note that I have set the wsgi to identify python by the extension .py, normally .wsgi is used, I think this is some kind of tradition, or old charter, or something.
Apache on Debian runs as the user www-data, for access to the serial port and GPIO on the Raspberry Pi you will need to add that user to the relevant groups. Do not run apache as root, while this is not so important when on the Pi it is good practice to avoid.
Edit /etc/rc.local and add these two lines to the end of the file:
chgrp -R dialout /sys/class/gpio
chmod -R g+rw /sys/class/gpio
when you reboot the computer, group permissions will be set to dialout on the gpio
add www-data to the dialout group
# usermod -a -G dialout www-data
Update: the /etc/rc.local method does not work, instead I have found found a tool called GPIO Admin and they have also written a Python GPIO API for it. Currently it is under development, but once installed add apache to the gpio group:
# usermod -a -G gpio www-data
and the web server will have access to the gpio pins
enable the module (it may of been enabled when installed) and restart apache
# a2enmod wsgi
# /etc/init.d/apache2 restart
To test your wsgi installation place the following file into your apache root directory /var/www as myinfo.py and load it using your web browser, http://<pi’s ip address>/myinfo.py .
Part 2: Using The Flask Framework
Here I have made a simple demonstration of how to use Flask, it consists of a wrapper, demo.py, the actual program coreDemo.py and some html to process, demo.html. It does not show how to use the GPIO or UART. The wrapper is used to capture error messages and conveniently display them in the web browser. Again save these files into your apache root directory, /var/www and load it using your web browser, http://<pi’s ip address>/demo.py
Now all you have to do is open the port 80 forwarding on your router, and everyone in the world can make your little buzzer project make noises at two in the morning.