函数内置方法

内置方法的特点:一定有某一个语法或者一种写法会自动触发这个方法

__init__ :实例化

__init__是初始化方法

class Student():
    def __init__(self,name,age):
        self.name = name
        self.age = age
wl = Student('wanglan',18)
print(wl.name)
print(wl.age)

结果:
wanglan
18

__new__

实例化的过程:创建一个内存空间,执行init,传入self,返回self,内存空间就是__new__创建的,__new__shi构造方法

class Student(object):
    def __init__(self,name,age):
        self.name = name
        self.age = age
wl = Student('wanglan',18)
print(wl.name)
print(wl.age)
print(wl.__dict__)

#结果:
wanglan
18
{'name': 'wanglan', 'age': 18}

#程序正常执行了


#加上__new__方法

class Student(object):
    def __new__(cls, *args, **kwargs):
        print('我执行了')
    def __init__(self,name,age):
        self.name = name
        self.age = age
wl = Student('wanglan',18)
print(wl.name)
print(wl.age)
print(wl.__dict__)
结果:
我执行了
Traceback (most recent call last):
    print(wl.name)
AttributeError: 'NoneType' object has no attribute 'name'

Process finished with exit code 1

#报错啦


#调用方法
class Student:
    def __new__(cls, *args, **kwargs):
        ret = object.__new__(cls)
        print('ret',ret)
        return ret
    def __init__(self,name,age):
        self.name = name
        self.age = age
wl = Student('wanglan',18)
print('wl',wl)
print(wl.name)
print(wl.age)

结果:
ret <__main__.Student object at 0x000000000290AB70>
wl <__main__.Student object at 0x000000000290AB70>
wanglan
18

class Student(object):
    flag = None
    def __new__(cls, *args, **kwargs):
        if cls.flag is None:
            cls.flag =object.__new__(cls)  #这一句自走一次
        return cls.flag
    def __init__(self,name,age):
        self.name = name
        self.age = age
wl = Student('wanglan',18)
xm = Student('xiaoming',18)
print(wl)
print(xm)
print(wl.name)
print(xm.name)

结果:
<__main__.Student object at 0x00000000028DAB70> #地址一样
<__main__.Student object at 0x00000000028DAB70>
xiaoming #只开辟了一块空间,name的值被覆盖了,值为最后的name
xiaoming

__call__

对象()会触发__call__方法

class Student():
    def __init__(self,name,age):
        self.name = name
        self.age = age
wl = Student('wanglan','18')
print(callable(Student))
print(callable(wl))  # wl不能被调用

结果:
True
False

# 加入__call__方法
class Student():
    def __init__(self,name,age):
        self.name = name
        self.age = age
    def __call__(self, *args, **kwargs):
        print('我被调用了')
wl = Student('wanglan','18')
print(callable(Student))
print(callable(wl))  # wl可以被调用了
wl() #调用

结果:
True
True
我被调用了

__del__:析构

class File(object):
    def __init__(self,file_name):
        self.f = open('file_name') #打开一个文件
    def read(self):
        self.f.read(1024)
    def __del__(self): # 对象使用的一些操作系统的资源的归还工作/收尾工作
        self.f.close() 
my_f = File()
my_f.read()

__str__和__repr__

class Course:
    def __init__(self,name,price,period,teacher):
        self.name = name
        self.price = price
        self.period = period
        self.teacher = teacher
    def __str__(self):  # 必须有返回值,必须返回一个str类型
        return '%s,%s,%s,%s'%(self.name,self.price,self.period,self.teacher)
python = Course('python',19800,'6 months','hehe')
linux = Course('linux',16800,'5 months','haha')
print(python) #使用__str__方法,打印对象时不会在打印地址,打印的是值
print(linux)
print('课程展示 : %s'%python)

__repr__ 是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):  # 必须有返回值,必须返回一个str类型
        return 'repr --> : %s,%s,%s,%s'%(self.name,self.price,self.period,self.teacher)
    def __str__(self):  # 必须有返回值,必须返回一个str类型
        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)
print(linux)



class Course:
    def __init__(self,name,price,period,teacher):
        self.name = name
        self.price = price
        self.period = period
        self.teacher = teacher
    def __repr__(self):  # 必须有返回值,必须返回一个str类型
        return 'repr --> : %s,%s,%s,%s'%(self.name,self.price,self.period,self.teacher)
    def __str__(self):  # 必须有返回值,必须返回一个str类型
        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('%r'%python)
print('%s'%python)
print(str(python))
print(repr(python))

item系列

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'])  # ==> 调用getitem
print(python['price'])  # ==> 调用getitem
python['name'] = 'python2.0'
print(python.name)
del python.name
del python['name']
print(python.__dict__)

__len__

class A:
    def __init__(self):
        self.a = 1
        self.b = 2

    def __len__(self):
        return len(self.__dict__)
a = A()
print(len(a))

__eq__

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('WL',20)
s2 = Student('WL',20)
print(s1 == s2)   # s1.__eq__(s2)
print(s1 is s2)   # s1.__eq__(s2)