Don’t check whether it is-a duck: check whether it quacks-like-a duck, walks-like-a duck, etc, etc, depending on exactly what subset of duck-like behavior you need to play your language-games with. (
comp.lang.python, Jul. 26, 2000)
— Alex Martelli
In this chapter, we will create a class to represent a multidimensional
Vector class—a significant step up from the two-dimensional
Vector2d of Chapter 9.
Vector will behave like a standard Python immutable flat sequence. Its elements will be floats, and it will support the following by the end of this chapter:
We’ll also implement dynamic attribute access with
__getattr__ as a way of replacing the read-only properties we used in
Vector2d—although this is not typical of sequence types.
The code-intensive presentation will be interrupted by a conceptual discussion about the idea of protocols as an informal interface. We’ll talk about how protocols and duck typing are related, and its practical implications when you create your own types.
Let’s get started.