The Object Oriented: metaclass, reflection, the method bis

1. Moto类

class A:
    pass
obj = A()

print(type('abc'))      # <class 'str'>
print(type([1,2,3]))    # <class 'list'>
print(type((22,33)))    # <class 'tuple'>

# type 获取对象从属于的类
print(type(A))      # <class 'type'>
print(type(str))    # <class 'type'>
print(type(dict))   # <class 'type'>

Everything in python objects, classes in a sense is an object, python in their definition of the class, as well as most of the built-in classes, are the type metaclass (building category) instantiated come

# type 与 object 的关系.
# print(type(object)) object类是type类的一个实例.
# object类是type类的父类.

print(issubclass(type,object))

2. Reflector

Examples of object classes modules other modules of the present

hasattr getattr setattr delattr

2.1 instance object:

class A:

    country = '中国'

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

    def func(self):
        print('in A func')

obj = A('赵海狗',47)

# hasattr
print(hasattr(obj,'name'))
print(hasattr(obj,'country'))
print(hasattr(obj,'func'))
# getattr
print(getattr(obj,'name'))
print(getattr(obj,'func'))
f = getattr(obj,'func')
f()
print(getattr(obj,'sex',None))
if hasattr(obj,'name'):
    getattr(obj,'name')

# setattr,delattr # 用的很少
obj.sex = '公'
print(obj.sex)
setattr(obj,'sex','公')
print(obj.__dict__)
delattr(obj,'name')
print(obj.__dict__)

2.2 angle from the class:

class A:

    country = '中国'

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

    def func(self):
        print(self)
        print('in A func')

# if hasattr(A,'country'):
#     print(getattr(A,'country'))


if hasattr(A,'func'):
    obj = A('赵海狗', 26)
    getattr(obj,'func')()
    getattr(A,'func')(obj)

Other modules from 2.3:

import tbjx
print(getattr(tbjx,'name'))
getattr(tbjx,'func')()

# 1. 找到tbjx对象 的C类,实例化一个对象.
print(getattr(tbjx,'C'))
obj = getattr(tbjx,'C')('123')
# 2. 找到tbjx对象 的C类,通过对C类这个对象使用反射取到area.
print(getattr(tbjx.C,'area'))
# 3. 找到tbjx对象 的C类,实例化一个对象,对对象进行反射取值.
obj = getattr(tbjx,'C')('赵海狗')
print(obj.name)
print(getattr(obj,'name'))
# 从当前模块研究反射:
a = 666

def func1():
    print('in 本模块这个对象')

def func1():
    print('in func1')

def func2():
    print('in func2')

def func3():
    print('in func3')

def func4():
    print('in func4')

import sys
# print(sys.modules[__name__])
# print(getattr(sys.modules[__name__],'a'))
# getattr(sys.modules[__name__],'func1')()
# getattr(sys.modules[__name__],'func2')()
# getattr(sys.modules[__name__],'func3')()

func_lst = [f'func{i}' for i in range(1,5)]
print(func_lst)
for func in func_lst:
    getattr(sys.modules[__name__],func)()

class User:

    user_list = [('login','登录'),('register','注册'),('save', '存储')]

    def login(self):
        print('欢迎来到登录页面')

    def register(self):
        print('欢迎来到注册页面')

    def save(self):
        print('欢迎来到存储页面')


while 1:
    choose = input('请输入序号: \n1: 登录\n2: 注册\n3: 存储\n').strip()  # 1
    obj = User()
    getattr(obj, obj.user_list[int(choose)-1][0])()  # getattr(obj,'login')

3. The difference between the function and method

def func1():
    pass

class A:
    def func(self):
        pass

# 1. 通过打印函数名的方式区别什么是方法,什么是函数. (了解)
print(func1)
print(A.func)  # 通过类名调用的类中的实例方法叫做函数.
obj = A()
print(obj.func) # 通过对象调用的类中的实例方法叫方法.

# 2. 可以借助模块判断是方法还是函数.

from types import FunctionType
from types import MethodType

def func():
    pass

class A:
    def func(self):
        pass

obj = A()


print(isinstance(func,FunctionType))  # True
print(isinstance(A.func,FunctionType))  # True
print(isinstance(obj.func,FunctionType))  # False
print(isinstance(obj.func,MethodType))  # True

# 总结:
# python 中一切皆对象, 类在某种意义上也是一个对象,python中自己定义的类,
# 以及大部分内置类,都是由type元类(构建类)实例化得来的.
# python 中一切皆对象, 函数在某种意义上也是一个对象,函数这个对象是从FunctionType这个类实例化出来的.
# python 中一切皆对象, 方法在某种意义上也是一个对象,方法这个对象是从MethodType这个类实例化出来的.

class A:
    @classmethod
    def func(cls,a):
        pass

    @staticmethod
    def func1():
        pass

# A.func(222)
# A.func()
# obj = A()
# obj.func()

# 总结: 如何判断类中的是方法还是函数.
# 函数都是显性传参,方法都是隐性传参.

4. The method of the special-bis

Special Double Down method: python was originally developed in this language programmer's source code used.
Str: We can not be easily used with caution.
Double Down method: you do not know what you did to trigger a Double Down method.

4.1__len__

class B:

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

    def __len__(self):
        print(self.__dict__)

        return len(self.__dict__)  # 2

b = B('leye',28)

print(len(b))
# dict
print(len({'name': 'leye', 'age': 28}))

4.2__len__

class A(object):

    pass

obj = A()

print(hash(obj))
print(hash('fdsaf'))

4.3__str__

class A:

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

    def __str__(self):
        print(666)
        return f'姓名: {self.name} 年龄: {self.age}'

a = A('赵海狗',35)
b = A('李业',56)
c = A('华丽',18)
# 打印对象触发__str__方法
print(f'{a.name}  {a.age}')
print(f'{b.name}  {b.age}')
print(f'{c.name}  {c.age}')
print(a)
print(b)
print(c)
# 直接str转化也可以触发.
print(str(a))

4.4__repr__

print('我叫%s' % ('alex'))
print('我叫%r' % ('alex'))
print(repr('fdsaf'))

class A:

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

    def __repr__(self):
        print(666)
        return f'姓名: {self.name} 年龄: {self.age}'

a = A('赵海狗',35)
b = A('李业',56)
c = A('华丽',18)
# print(a)
print(repr(a))

4.5__call__

__call__方法  ***
对象() 自动触发对象从属于类(父类)的__call__方法
class Foo:

    def __init__(self):
        pass

    def __call__(self, *args, **kwargs):
        print('__call__')

obj = Foo()
obj()

4.6__eq__

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

    def __eq__(self,obj):
        # if  self.a == obj.a and self.b == obj.b:
        #     return True
        return True
x = A()
y = A()
print(x == y)
x = 1
y = 2
print(x+y)

4.7__del__

__del__析构方法

class A:

    def __del__(self):
        print(666)

obj = A()
del obj

4.8__new__

# __new__ *** new一个对象  构造方法

class A(object):

    def __init__(self):

        self.x = 1
        print('in init function')

    def __new__(cls, *args, **kwargs):
        print('in new function')
        return object.__new__(A)  # object 342534

# 对象是object类的__new__方法 产生了一个对象.
a = A()

# 类名()
# 1. 先触发 object的__new__方法,此方法在内存中开辟一个对象空间.
# 2. 执行__init__方法,给对象封装属性.

print(a)

# python中的设计模式: 单例模式

# 一个类只允许实例化一个对象.
class A:
    pass

obj = A()
print(obj)
obj1 = A()
print(obj1)
obj2 = A()
print(obj2)

# 手写单例模式
class A:
    __instance = None

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

    def __new__(cls,*args,**kwargs):
        if not cls.__instance:
            cls.__instance = object.__new__(cls)
        return cls.__instance

obj = A('alex')
print(obj)
obj1 = A('李业')
print(obj1.name)
print(obj.name)