第三章魔法函数

 1 class Company(object):
 2     def __init__(self, employee_list):
 3         self.employee = employee_list
 4 
 5     # python编译器自动调用，使得可以在for in循环中使用
 6     def __getitem__(self, item):
 7         return self.employee[item]
 8 
 9 
10 company = Company(["tom", "bob", "jane"])
11 for em in company:
12     print(em)       # tom bob jane

 1 class Company(object):
 2     def __init__(self, employee_list):
 3         self.employee = employee_list
 4 
 5     # python编译器自动调用，使得可以在for in循环中使用
 6     def __getitem__(self, item):
 7         return self.employee[item]
 8 
 9     # python编译器自动调用，获得长度
10     # def __len__(self):
11     #     return len(self.employee)
12 
13 
14 company = Company(["tom", "bob", "jane"])
15 for em in company:
16     print(em)       # tom bob jane
17 
18 # __getitem__处理切片的数据可以得到len，不可以处理没有切片的数据
19 company1 = company[:2]
20 
21 # 步骤：
22 # 1.查找否有__len__
23 # 2.没有__len__再查看数据是否切片并且是否有__getitem__
24 # 3.有则可以获得len，如果数据没有切片则会报错
25 print(len(company1))    # 2

 1 class Company(object):
 2     def __init__(self, employee_list):
 3         self.employee = employee_list
 4 
 5     # 在对象格式化时调用
 6     def __str__(self):
 7         return ",".join(self.employee)
 8 
 9     # 在开发模式下调用
10     def __repr__(self):
11         return ",".join(self.employee)
12 
13 
14 company = Company(["tom", "bob", "jane"])
15 # 对象格式化
16 print(company)  # tom,bob,jane
17 # 开发模式:cmd或notebook中调用
18 company     # tom,bob,jane

 1 class MyVector(object):
 2     def __init__(self, x, y):
 3         self.x = x
 4         self.y = y
 5 
 6     def __add__(self, other):
 7         re_vector = MyVector(self.x + other.x, self.y + other.y)
 8         return re_vector
 9 
10     def __str__(self):
11         return "x:{x},y:{y}".format(x=self.x, y=self.y)
12 
13 
14 vec1 = MyVector(1, 2)
15 vec2 = MyVector(3, 4)
16 print(vec1 + vec2)  # x:4,y:6