Python学习笔记-初级（五）：面向对象

一、问题背景

“Python语言导论“课程作业：

1、  编写平面坐标处理的类，其中，需满足如下要求：

(1)   有“__eq__”方法（def __eq__(self, other):），若坐标被认为是平面上的同一个点则返回真（即有同样的x，y坐标）。
(2) 定义一个特殊方法__repr__（def __repr__(self):），能够输出形式如“Coordinate(1, 8)”的坐标。
(3) 完成如下操作：
* 创建一个坐标为（1，8）的对象
* 分别用str方法和repr方法显示该对象
* 再创建一个坐标为（1，8）的对象
* 判断这两个对象是否相等？

2、  创建一个新类表示整数集合
(1)   初始时集合为空
(2)   每个特定的整数只能在集合中出现一次（注：必须在方法中强制实现）
(3)   内部数据表示：用一个列表存储集合中的元素 
(4)   接口
* insert(e)：若整数e不存在，则插入e到集合中
* member(e)：若整数e在集合中返回True，否则返回False
* remove(e)：从集合中删除整数e，若不存在则出错

(5)   定义一个方法intersect(self, other)，返回一个新的intSet，包含同时出现在两个集合中的元素。换句话说，
s1.intersect(s2)，将返回同时包含在s1和s2中元素的新intSet。若s1和s2没有共同的元素该如何处理？

(6)   增加一个特殊方法__len__(self)，若调用len(s)，将返回s中元素的个数。

二、代码

1、  coordinate.py: 

<span style="font-size:14px;">'''
Author: WJT
Date: 11/4/2016

Function: deal with the coordinate of the points in a plane
'''

# class Coordinate to deal with the coordinate of the point in a plane
class Coordinate(object):
    # construction function
    def __init__(self, x, y):
        self.x = x
        self.y = y
    
    # public function for getting the coordinate x
    def getX(self):
        return self.x
    
    # public function for getting the coordinate y
    def getY(self):
        return self.y

    # private function for specific format print
    # overload of inner function "str" 
    def __str__(self):
        return '<' + str(self.getX()) + ',' + str(self.getY()) + '>'

    # private function for comparing two Coordinate objects
    # called implicitly when comparing
    def __eq__(self, other):
        if ((self.x == other.x) and (self.y == other.y)):
            return True
        else:
            return False
            
    # private function for specific format print
    # overload of inner function "repr" 
    def __repr__(self):
        return 'Coordinate<' + str(self.x) + ', ' +  str(self.y) + '>'

# test bench 
if __name__ == '__main__':
    obj1 = Coordinate(1, 8)
    print(str(obj1))
    print(repr(obj1))
    obj2 = Coordinate(1, 8)
    print(obj1 == obj2)
</span>

2、  intSet.py：

'''
Author: WJT
Date: 11/4/2016

Function: class for integer set
'''

class intSet(object):
    """
    An intSet is a set of integers
    The value is represented by a lis of ints, self.vals.
    Each int in the set occurs in self.vals exactly once.
    """

    def __init__(self):
        """Create an empty set of integers"""
        self.vals = []

    def insert(self, e):
        """Assumes e is an integer and insert e into self.vals"""
        if not e in self.vals:  # e not in self.vals
            self.vals.append(e)

    def member(self, e):
        """Assumes e is an integer
        return True if e is in self and False otherwise"""
        
        return e in self.vals

    def remove(self, e):
        """Assumes e is an integer and remove e from self
        Raise ValueError if e is not in self"""
        # try-except statements to deal with error
        try:
            self.vals.remove(e)
        except:
            raise ValueError(str(e) + 'not found')

    def __str__(self):
        "return a string representation of self"
        self.vals.sort()
        return '{' + ','.join([str(e) for e in self.vals]) + '}'

    def intersect(self, other):
        newSet = intSet()
        for i in self.vals:
            if other.member(i):
                newSet.insert(i)
        return newSet

    # private function for getting length
    # overload of inner funtion "len"
    def __len__(self):
        return len(self.vals)


# test bench
if __name__ == '__main__':
    obj_1 = intSet()
    for i in range(0, 10):
        obj_1.insert(i)
  
    obj_2 = intSet()
    for i in range(0, 6):
        obj_2.insert(i)

    # display length 
    print("length of obj_1: " + str(len(obj_1)))
    print("length of obj_2: " + str(len(obj_2)))

    # display intersection of two sets
    print(obj_1.intersect(obj_2))
    

三、运行结果

1、  coordinate.py：

2、  intSet.py：