Decision Making
===============

One of the key features of any programming language is the ability to decide
whether to run a segment of code. This means you can execute a set of
statements *only if* a given condition is met.

.. admonition:: Example

   Consider an application that reminds you when you have an overdue book. The
   app sends you a message *only if* the due date has passed and you have not
   returned the book.

The *condition* in the example above depends on the status of the book. If the
condition is true (the book is overdue), a message gets sent. If the condition
is false, then the app does not pester you.

In general, we set up decision making in Python by using the following
structure:

.. sourcecode:: Python
   :linenos:

   if condition_is_true:
      # Run this code
   else:
      # Run this other code

We will dive into the details soon, but first we need to understand how Python
determines if a condition is true or false.