Programming basics in Python for teachers

A good teacher does not draw out; he gives out, and what he gives out is love. And by love I mean approval, or if you like, friendliness, good nature. The good teacher not only understands the child: he approves of the child.

There are two ways of constructing a software design. One way is to make it so simple that there are obviously no deficiencies. And the other way is to make it so complicated that there are no obvious deficiencies.

Beware of bugs in the above code; I have only proved it correct, not tried it.