3 Function Definitions

Function definitions are a way to decompose a large problem into smaller problems. Mathematicians have been doing this for centuries. It's a way to package our Python programming into intellectually manageable chunks.

We'll look at a number of function definition techniques in these recipes. This will include ways to handle flexible parameters and ways to organize the parameters based on some higher-level design principles.

We'll also look at the typing module and how we can create more formal annotations for our functions. We will start down the road toward using the mypy project to make more formal assertions about the data types in use.

In this chapter, we'll look at the following recipes:

• Function parameters and type hints
• Designing functions with optional parameters
• Type hints for optional parameters
• Using super flexible keyword parameters
• Forcing keyword-only arguments with the * separator
• Defining position-only parameters with the / separator
• Writing hints for more complicated types
• Picking an order for parameters based on partial functions
• Writing clear documentation strings with RST markup
• Designing recursive functions around Python's stack limits
• Writing testable scripts with the script library switch