How do I rerun a progrom outside the shell?

[Miguel Valenzue]

I wrote a very basic program to calculate the slope of a pipe

firstElev = input ("Enter first elevation")
secondElev = input ("Enter second elevation")
length = input ("Enter Length")

promil = ((firstElev - secondElev)/length)*1000

print "Promil =",promil

Currently I run the program in the python shell and have to run it every time I need it to calculate the slope.
This can be tedious when I have many slopes to calculate.
How can I:
1. Have the program run outside the shell in it's own window
2. Have the program keep running until I type something like 'quit'?