Python超详细讲解元类的使用

# object 为顶层基类
class Work(object):
    a = 100
Mywork = Work()   # 实例化
print(Mywork )   # Mywork 是 Work 所创建的一个对象  <__main__.Work object at 0x101eb4630>
print(type(Mywork))    # <class '__main__.Work'>
print(type(Work))    # 类型为元类 <class 'type'>

class type(object):
"""
type(object_or_name, bases, dict)
type(object) -> the object's type
type(name, bases, dict) -> a new type
"""
	# 实例化
	def __init__(cls, what, bases=None, dict=None): # known special case of type.__init__
	     """
	     type(object_or_name, bases, dict)
	     type(object) -> the object's type
	     type(name, bases, dict) -> a new type
	     # (copied from class doc)
	     """
	     pass
	# 创建类    
	@staticmethod     # known case of __new__
    def __new__(*args, **kwargs):   # real signature unknown
        """ 
        Create and return a new object.  See help(type) for accurate signature. 
        （创建并返回一个新对象）
        """
        pass

a = 100
b = "100"
c = [11,22,33]
print(type(a))    # ======》 <class 'int'>
print(type(b))    # ======》 <class 'str'>
print(type(c))    # ======》 <class 'list'>

# 通过 class 定义类
class Myclass(object):
    a = 100
    b = 200
# 通过type创建的类(动态创建类)
Myclass1 = type("Myclass1",(object,),{"a":"100","b":"200"})
print(Myclass)
print(Myclass1)

def work(self):
    print("这是实例方法——————work————————")
# 定义类属性值
def init_method(self, aa, bb, cc):
    self.aa = aa
    self.bb = bb
    self.cc = cc
# 通过type创建的类(动态创建类)
Myclass2 = type("Myclass2",(object,),{"a":"100","b":"200","work":work,"work_1":work_1,"__init__":init_method})
m = Myclass2(11,22,33)
m.work()
print(m.aa, m.bb, m.cc)

# 定义一个类继承type
class Mytest(type):
	# 重写new方法
    def __new__(cls, type_name, bases, atter, *args, **kwargs):
        new_cls = super().__new__(cls,type_name, bases, atter)         
        return new_cls      # 返回新的类
M2 = Mytest("M2",(Mytest,),{"atter":100})
print(M2)     # =====》  <class '__main__.M2'>

class Myclass(type):
    """自定义的元类"""
    def __new__(cls, type_name, bases, attrs, *args, **kwargs):
        new_cls = super().__new__(cls, type_name, bases, attrs)
        print("这个是Myclass:", type_name, bases, attrs, )
        return new_cls
# 通过metaclass=xxxx   继承自定义元类
class Inherited_class(metaclass=Myclass):
    a = 100
    b = 200
print(type(Inherited_class))  # ======》 <class '__main__.Myclass'>