A key ingredient in writing good code is avoiding redundancy. In object-oriented programming (OOP), methods and functions are important tools that we can use to avoid writing redundant code. Remember the sorted() example in the previous chapter. The sorted() function is generic enough that it can be used to sort more than one data structure (lists, tuples, and namedtuples) using arbitrary keys. That's the definition of a good function.

Functions such as sorted() demonstrate the ideal case. In reality, we cannot always write 100 percent generic code. There are many algorithms that have some (but not all) common steps. A good example is breadth-first search (BFS) and depth-first search (DFS), two popular algorithms used in graph searching. Assume that we are asked to implement BFS and DFS in Python. Initially, we come up with two independent implementations (the graph.py file). The functions bfs() and dfs() return a tuple of (True, path) if a path between start...