The Template pattern

The Template pattern (sometimes called the Template method) is useful for removing duplicate code; it's intended to support the Don't Repeat Yourself principle we discussed in Chapter 5, When to Use Object-Oriented Programming. It is designed for situations where we have several different tasks to accomplish that have some, but not all, steps in common. The common steps are implemented in a base class, and the distinct steps are overridden in subclasses to provide custom behavior. In some ways, it's like the Strategy pattern, except similar sections of the algorithms are shared using a base class. Here it is in the UML format:

Figure 12.11: The Template pattern

A Template example

Let's create a car sales reporter as an example. We can store records of sales in an SQLite database table. SQLite is the built-in database engine that allows us to store records using SQL syntax. Python includes SQLite in its standard...