1. 概念
1.1 MetaClass作用:用来指定当前类由谁来创建(默认type创建)
2. 如何用metaclass?
第一种为Python3, 第二种为Python2/3
class Foo(metaclass=type):
pass
class Foo(object):
__metaclass__ = type
3. 例子
3.1 MyType('Base', (object,), {}) 是由MyType创建; metaclass=MyType
3.2 type可以创建类时,metaclass=type;MyType创建类时,metaclass=MyType
3.3 Base = MyType('Base', (object,), {}) 等价于 Base(metaclass=MyType)
# 自定义元类
class MyType(type):
def __init__(self, *args, **kwargs):
super(MyType, self).__init__(*args, **kwargs)
def __call__(cls, *args, **kwargs):
print('xxxx')
return super(MyType, cls).__call__(*args, **kwargs)
# 用元类创建Base类,调用了元类的__call__
Base = MyType('Base', (object,), {})
Base()
print(Base) #<class '__main__.Base'>
print(type(Base)) #<class '__main__.MyType'>
# Foo继承Base类,也是指向同一个元类
class Base(metaclass=MyType):
pass
class Foo(Base):
pass
obj = Foo()
结果
xxxx
<class '__main__.Base'>
<class '__main__.MyType'>
xxxx