A very simple application

We shall start with the simplest possible application, a "scientific hello world program", where the task is to read a number and write out "Hello, World!" followed by the sine of the number. This application has one input variable and a line of text as output.

Our first implementation reads the input from the command line and writes the results to the terminal window: 

#!/usr/bin/env python
import sys, math
r = float(sys.argv[1])
s = math.sin(r)
print 'Hello, World! sin(%g)=%g' % (r, s)
In the terminal we can exemplify the program 

Terminal> python hw.py 1.2
Hello, World! sin(1.2)=0.932039
The task of the web version of this program is to read the r variable from a web page, compute the sine, and write out a new web page with the resulting text.