伯克利 CS61A 课堂笔记 09 —— Data Abstraction

本系列为加州伯克利大学著名 Python 基础课程 CS61A 的课堂笔记整理，全英文内容，文末附词汇解释。

目录

01 Data Abstraction 数据抽象

Ⅰ Rational Numbers

Ⅱ Rational Number Arithmetic

02 Pairs 对

Ⅰ Representing Pairs Using Lists

Ⅱ Reducing to Lowest Terms

03 Abstraction Barriers 抽象障碍

04 Data Representations 数据表示

Ⅰ What is Data?

Ⅱ Demo

Ⅲ Rational Data Abstraction Implemented as Functions

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01 Data Abstraction 数据抽象

Compound objects combine objects together:

​        A date: a year, a month, and a day.

​        A geographic position: latitude and longitude.

An abstract data type lets us manipulate compound objects as units.

Isolate two parts of any program that uses data:

​        How data are represented (as parts).

​        How data are manipulated (as units).

Data abstraction: A methodology by which functions enforce an abstraction barrier between representation and use.

Ⅰ Rational Numbers

Exact representation of fractions is a pair of integers. However, as soon as division occurs, the exact representation may be lost !

Assume we can compose and decompose rational numbers:

Ⅱ Rational Number Arithmetic

#最上层

def mul_rational(x, y):
    """Multiply rational numbers x and y."""
    return rational(numer(x) * numer(y),
                    denom(x) * denom(y))

def add_rational(x, y):
    """Add rational numbers x and y."""
    return rationa