Advanced Python 3 Programming Techniques

Chapter 5. Local and Recursive Functions

It is often useful to have one or more small helper functions inside another function. Python allows this without formality—we simply define the functions we need inside the definition of an existing function. Such functions are often called nested functions or local functions.

One common use case for local functions is when we want to use recursion. In these cases, the enclosing function is called, sets things up, and then makes the first call to a local recursive function. Recursive functions (or methods) are ones that call themselves. Structurally, all directly recursive functions can be seen as having two cases: the base case and the recursive case. The base case is used to stop the recursion. ...