Python 面向对象4-特殊成员

1.__call__

　　类后面加()表示对象，执行__init__方法，对象后面加()执行__call__方法

class Foo:

    def __init__(self,name):
        self.name = name
        print ("init func")

    def __call__(self):
        print ("call func")

obj = Foo("Alex")
obj()

如果不定义__call__方法，那么执行obj()报错：

TypeError: ‘Foo‘ object is not callable

如果定义了__call__方法，那么在对象后面加()则执行__call__方法。

2.__str__

　　有一段代码如下：

class Foo:

    def __init__(self,name):
        self.name = name
        print ("init func")

    def __call__(self):
        print ("call func")
# class Bar(Foo):
#
#     def f3(self):
#         print (self.name)

obj = Foo("Alex")
print (obj)结果：　　<__main__.Foo object at 0x013349B0>

我们想打印一个对象(obj)的内容，但是返回了一个类的内存地址，通过__str__方法可以实现这样的需求

class Foo:

    def __init__(self,name):
        self.name = name

    def __call__(self):
        print ("call func")

    def __str__(self):
        return self.name

obj = Foo("Alex")
print (obj)结果：　　Alex

如果__init__方法中有多个字段，那么也可以利用字符串的拼接将结果返回回来

class Foo:

    def __init__(self,name,age):
        self.name = name
        self.age = age

    def __call__(self):
        print ("call func")

    def __str__(self):
        return "%s - %s" %(self.name,self.age)

obj = Foo("Alex",18)
print (obj)结果：　　Alex - 18

class Foo:

    def __init__(self,name,age):        self.name = name        self.age = age

    def __call__(self):        print ("call func")

    # def __str__(self):    #     return "%s - %s" %(self.name,self.age)

obj = Foo("Alex",18)# print (obj)ret = str(obj)print (ret)结果：　　<__main__.Foo object at 0x01D7F810>

如果没有__str__方法，那么str(返回)的类对象的内存地址，如果定义了__str__方法，在执行str(obj)的时候，自动调用__str__方法。

class Foo:

    def __init__(self,name,age):
        self.name = name
        self.age = age

    def __call__(self):
        print ("call func")

    def __str__(self):
        return "%s - %s" %(self.name,self.age)

obj = Foo("Alex",18)
# print (obj)
ret = str(obj)
print (ret)结果：　　Alex - 18

3.__add__　

class Foo:

    def __init__(self,name,age):
        self.name = name
        self.age = age

    def __call__(self):
        print ("call func")
def __add__(self, other):
        return "%s - %s" %(self.name,other.age)
obj1 = Foo("Alex",18)
obj2 = Foo("Lily",15)

ret = obj1 + obj2
print (ret)结果:　　Alex - 15

__add__方法是对两个对象之间做加法，在做加法的时候系统自己调用该方法。

4.__dict__

__author__ = ‘Alex‘
#coding:utf-8

class Foo:

    def __init__(self,name,age):
        self.name = name
        self.age = age

    def __call__(self):
        print ("call func")

    # def __str__(self):
    #     return "%s - %s" %(self.name,self.age)

    def __add__(self, other):
        return "%s - %s" %(self.name,other.age)
obj1 = Foo("Alex",18)
obj2 = Foo("Lily",15)

print (obj1.__dict__)
print (obj2.__dict__)
print (Foo.__dict__)结果：　　

　　{‘age‘: 18, ‘name‘: ‘Alex‘}
　　{‘age‘: 15, ‘name‘: ‘Lily‘}
　　{‘__init__‘: <function Foo.__init__ at 0x013641E0>, ‘__doc__‘: None, ‘__module__‘: ‘__main__‘, ‘__call__‘: <function Foo.__call__ at 0x01364228>, ‘__add__‘: <function Foo.__add__ at 0x013640C0>, ‘__dict__‘: <attribute ‘__dict__‘ of ‘Foo‘ objects>, ‘__weakref__‘: <attribute ‘__weakref__‘ of ‘Foo‘ objects>}

5.__getitem__、__setitem__、__delitem__

class Foo:

    def __init__(self,name,age):
        self.name = name
        self.age = age

    def __call__(self):
        print ("call func")

    # def __str__(self):
    #     return "%s - %s" %(self.name,self.age)

    def __add__(self, other):
        return "%s - %s" %(self.name,other.age)

    def __getitem__(self, item):
        return item

    def __setitem__(self, key, value):
        pass

    def __delitem__(self, key):
        pass

obj1 = Foo("Alex",18)

ret = obj1[‘aaa‘]
print (ret)

obj1[‘bbb‘] = 456
ret1 = obj1[‘bbb‘]
print (ret1)

del obj1[‘bbb‘]
print (obj1[‘bbb‘])

对象的切片访问形式，例如obj1[1:4]

class Foo:

    def __init__(self,name,age):        self.name = name        self.age = age

    def __call__(self):        print ("call func")

    # def __str__(self):    #     return "%s - %s" %(self.name,self.age)

    def __add__(self, other):        return "%s - %s" %(self.name,other.age)

    def __getitem__(self, item):        if type(item) is str:            print (item)            return item        else:            print (item.start)            print (item.stop)            print (item.step)

    def __setitem__(self, key, value):        print (key.start)        print (key.stop)        print (key.step)        print (type(key),type(value))

    def __delitem__(self, key):        print (type(key))        print (key.start)        print (key.stop)        print (key.step)

obj1 = Foo("Alex",18)# ret = obj1[‘aaa‘]# ret = obj1[1:4:2]# obj1[1:4] = [11,22,33,44,55,66]del obj1[1:4]# print (ret)# print (ret)## obj1[‘bbb‘] = 456# ret1 = obj1[‘bbb‘]# print (ret1)## del obj1[‘bbb‘]# print (obj1[‘bbb‘])

6.__iter__

class Foo:

    def __iter__(self):
        return iter([11,22,33])

obj = Foo()
for item in obj:
    print (item)结果：　　11　　22　　33

如果一个对象可以被迭代，那么就可以执行for循环。被循环的对象默认调用__iter__方法，返回值必须是一个可以被迭代的对象。

class Foo:

    def __iter__(self):              #生成器生成一个可迭代的对象
        yield 11
        yield 22

obj = Foo()
for item in obj:
    print (item)结果：　　11　　22