双下方法(魔术方法内置方法)

关于内置方法的名字    
　　内置方法 双下方法  魔术方法
内置方法的特点
    一定有某一个语法或者一种写法自动触发这个方法

写法      触发      对应的内置方法
实例化
对象
del 对象
print(对象)
str(对象)
'%s'%对象
repr()
'%r'%对象
len(对象)
对象[canshu]
==

__call__
class Son():
    def __init__(self):
        pass
    def __call__(self, *args, **kwargs):
        print('被执行了')
a = Son()
a()
print(callable(a))  #查看某个变量能否被调用   返回的是True  就是能被调用
print(callable(Son))  #查看某个变量能否被调用   返回的是True  就是能被调用

__new__  构造方法,提供了一个类实例化对象的时候所有需要的内存空间
实例化的过程:创建一个内存空间  执行init,传self,返回self

class Dog():
    def __new__(cls, *args, **kwargs):
        dog_obj = object.__new__(cls)
        return dog_obj
    def __init__(self,name,age):
        self.name = name
        self.age = age
wc  = Dog('玩彩',8)
print(wc.name)


单例模式
class Dog:
    flag = None
    count = 0
    def __new__(cls, *args, **kwargs):
        if cls.flag is None:
            cls.flag = object.__new__(cls)
            cls.count += 1
            return cls.flag
        return cls.flag
    def __call__(self, *args, **kwargs):
        Dog.count += 1
        return Dog.count
a = Dog()
q = Dog()
print(a())



class Teacher:
    flag = None
    def __new__(cls, *args, **kwargs):
        if cls.flag is None:
            cls.flag = object.__new__(cls)    # 这一句话只能走一次
        return cls.flag
    def __init__(self,name):
        self.name = name

alex1 = Teacher('alex')
alex2 = Teacher('alex')
yuan = Teacher('yuan')
print(alex1.name)
print(yuan.name)


析构方法(了解)删除
执行del对象的时候出发__del__,在真正的删除alex对象之前,执行的方法__del__
如果我们自己不删除alex,name在程序的执行过程中或者最后垃圾回收机制会替你执行del alex

class Teacher:
    def __init__(self,name):
        self.name = name
    def __del__(self):
        print('执行我啦')
alex = Teacher('你还')
# del alex    #删除
print(alex.name)   #删除后执行将会报错

class Course():
    def __init__(self,name,price,period,teacher):
        self.name = name
        self.price = price
        self.teacher = teacher
        self.period = period
    def __str__(self):
        return '%10s%10s%20s%10s'% (self.name,self.price,self.period,self.teacher)
lst = []
python = Course('python',19800,'6 months','女神')
linux = Course('linux',19800,'6 months','女神')
print(python)
print(str(python))
print('课程显示: %s'%python)

lst.append(python)
lst.append(linux)
for i in  lst:
    print(i)

__repr__ str方法的备胎(有str调用str,没有str走repr)
class Course():
    def __init__(self,name,price,period,teacher):
        self.name = name
        self.price = price
        self.period = period
        self.teacher = teacher
    def __repr__(self):
        return 'repr>>>%s%s%s%s'%(self.name,self.price,self.period,self.teacher)
    def __str__(self):
        return 'str<<<<%s%s%s%s' % (self.name, self.price, self.period, self.teacher)
python = Course('python',19800,'6 months','baoyuan')
linux = Course('linux',16800,'5 months','oldboy')
print(python)

流畅的python:repr和str如果只能写一个的 就写 repr

class Course:
    def __init__(self,name,price,period,teacher):
        self.name = name
        self.price = price
        self.period = period
        self.teacher = teacher
    def __len__(self):
        return len(self.__dict__)
    def __getitem__(self,item):
        return self.__dict__[item]
    def __setitem__(self, key, value):
        self.__dict__[key] = value
    def __delitem__(self, key):
        self.__dict__.pop(key)

python = Course('python',19800,'6 months','baoyuan')
print(python.name)
print(python['name'])
python['name'] = '你好'
print(python['name'])
del python['teacher']
print(python.teacher)

class Ruler():
    def __init__(self,price,length,jingdu):
        self.length = length
        self.price = price
        self.jingdu = jingdu
    def __len__(self):
        return self.length
ret = Ruler(2.5,14,0.1)
print(len(ret))


class Student():
    def __init__(self,name,age):
        self.name = name
        self.age = age
    def __eq__(self, other):
        if self.name == other.name and self.age == other.age:
            return True
        return False
s1 = Student('锚',5)
s2 = Student('锚',5)
print(s1 == s2)
print(s1 is s2)
print(id(s1),id(s2))