第672页 | Learning Python | 阅读 ‧ 电子书库

Python and OOP

Let’s begin with a review—Python’s implementation of OOP can be summarized by three ideas:

Inheritance

Inheritance is based on attribute lookup in Python (in X.name expressions).

Polymorphism

In X.method, the meaning of method depends on the type (class) of X.

Encapsulation

Methods and operators implement behavior; data hiding is a convention by default.

By now, you should have a good feel for what inheritance is all about in Python. We’ve also talked about Python’s polymorphism a few times already; it flows from Python’s lack of type declarations. Because attributes are always resolved at runtime, objects that implement the same interfaces are interchangeable; clients don’t need to know what sorts of objects are implementing the methods they call.

Encapsulation means packaging in Python—that is, hiding implementation details behind an object’s interface. It does not mean enforced privacy, though that can be implemented with code, as we’ll see in Chapter 38. Encapsulation allows the implementation of an object’s interface to be changed without impacting the users of that object.