Writing and Running a Program
So far, we have used the shell to investigate Python. As you have seen, the shell will show you the result of evaluating an expression:
|||>>> 3 + 5 / abs(-2)|
In a program that is supposed to interact with a human, showing the result of every expression is probably not desirable behavior. (Imagine if your web browser showed you the result of every calculation it performed.)
How Does a Computer Run a Python Program?, explained that in order to save code for later use, you can put it in a file with a .py extension. You can then tell Python to run the code in that file rather than type commands in at the interactive prompt.
Here is a program that we wrote using IDLE and saved in a file ...