(董付国)Python 学习笔记---Python面向对象程序设计(3)
6.4.2 案例精选
- 例6-1:自定义数组。在MyArray.py文件中,定义了一个数组类,重写了一部分特殊方法以支持数组之间、数组与整数之间的四则运算以及内积、大小比较、成员测试和元素访问等运算符。
class MyArray: # 在内部封装/隐藏了一个列表
'''All the elements in this array must be numbers'''
def __IsNumber(self,n): #定义了一个私有的成员方法
return isinstance(n,(int,float,complex))
def __init__(self,*args): #类的构造方法,‘*’可变长度参数
if not args:
self.__value = [] #如果传值不是int,float,complex则给个空列表包装成数组
else:
for arg in args:
if not self.__IsNumber(arg):
print('All elements must be numbers')
return
self.__value = list(args)
#重载运算符+
#数组中每个元素都与数字n相加,或两个数组相加,返回新数组
def __add__(self,n):
if self.__IsNumber(n):
#数组中所有元素都与数字n相加
b = MyArray() #构建一个空数组
b.__value = [item+n for item in self.__value] #列表推导式
return b
elif isinstance(n,MyArray): #MyArray是一个数组类型
if len(n.__value) == len(self.__value):
c = MyArray()
c.__value = [i+j for i,j in zip(self.__value,n.__value)]
return c
else:
print('Length not equal')
else:
print('Not supported')
#重载运算符-
#数组中每个元素都与数字n相减,返回新数组
def __sub__(self,n):
if not self.__IsNumber(n):
#减法对于n的类型和数字类型之间不支持操作
print('- operating with ',type(n),'and number type is not supported.')
return
b = MyArray()
b.__value = [item-n for item in self.__value]
return b
#重载运算符*
#数组中每个元素都与数字n相乘,返回新数组
def __mul__(self,n):
if not self.__IsNumber(n):
#乘法对于n的类型和数字类型之间不支持操作
print('* operating with ',type(n),'and number type is not supported.')
return
b = MyArray()
b.__value = [item*n for item in self.__value]
return b
#重载运算符/
#数组中每个元素都数字n相除,返回新数组
def __truediv__(self,n):
if not self.__value(n):
#除法对于n的类型和数字不支持操作
print(r'/ operating with',type(n),'and number is not supported.')
return
b = MyArray()
b.__value = [item/n for item in self.__value]
return b
#重载运算符//
#数组中每个元素都与数字n整除,返回新数组
def __floordiv__(self,n):
if not isinstance(n,int):
print(n,' in not an integer')
return
b = MyArray()
b.__value = [item//n for item in self.__value]
#重载运算符%
#数组中每个元素都数字n求余数,返回新数组
def __mod__(self,n):
if not self.__value(n):
print(r'% operating with',type(n),'and number type is not supported.')
return
b = MyArray()
b.__value = [item%n for item in self.__value]
return b
#重载运算符**
#数组中每个元素都数字n求幂运算,返回新数组
def __pow__(self,n):
if not self.__value(n):
print(r'** operating with',type(n),'and number type is not supported.')
return
b = MyArray()
b.__value = [item**n for item in self.__value]
return b
def __len__(self):
return len(self.__value)
#直接使用该对象作为表达式来查看对象的值
def __repr__(self):
return repr(self.__value)
#支持使用print()查看对象的值
def __str(self):
return str(self.__value)
#追加元素
def append(self,v):
assert self.__IsNumber(v),'Only number can be appended.' #如果v满足条件则返回数组,否则抛出异常
#获取指定下标的元素值,支持使用列表或元组指定多个下标
def __getitem__(self,index):
length = len(self.__value)
#如果指定单个整数作为下标,直接返回元素值
if isinstance(index,int) and 0<=index<=length:
return self.__value[index]
elif isinstance(index,(list,tuple)):
for i in index:
if not (isinstance(i,int) and 0<=i<=length):
return 'index error'
result = []
for item in index:
result.append(self.__value[item])
return result
else:
return 'index error'
#修改元素值,支持使用列表或元组指定多个下标,同时修改多个元素值
def __setitem__(self,index,value):
length = len(self.__value)
#如果下标合法,则直接修改元素
if isinstance(index,int) and 0<=index<=length:
self.__value[index] = value
#支持使用列表或元组指定多个下标
elif isinstance(index,(list,tuple)):
for i in index:
if not isinstance((i,int) and 0<=i<=length):
raise Exception('index error')
#如果下标和给的值都是元组或列表,并且个数一样,则分别为多个下标的元素修改值
if isinstance(value,(list,tuple)):
if len(index) == len(value):
for i,v in enumerate(index):
self.__value[v] = value[i]
else:
raise Exception('value and index must be of the same length')
#如果指定多个下标和一个普通值,则把多个元素修改为相同的值
elif isinstance(value,(int,float,complex)):
for i in index:
self.__value[i] = value
else:
raise Exception('value error')
else:
raise Exception('index error')
#支持成员测试运算符in,测试数组中是否包含某个元素
def __contains__(self,v):
return v in self.__value
#模拟向量内积
def dot(self,v):
if not isinstance(v,MyArray):
print(v,' must be an instance of MyArray.')
return
if len(v) != len(self.__value):
print('The size must be equal.')
return
return sum([i*j for i,j in zip(self.__value,v.__value)])
#重载运算符==,测试两个数组是否相等
def __eq__(self,v):
assert isinstance(v,MyArray),'wrong type'
return self.__value == v.__value
#重载运算符<,比较两个数组大小
def __lt__(self,v):
assert isinstance(v,MyArray),'wrong type'
return self.__value < v.__value
if __name__ == '__main__':
print('Please use me as a module.')