- 源码学习
class SetterAwareType(type): # 元类
def __new__(cls, *args):
# print('in SetterAwareType __new__')
# print(type(type.__new__(cls, 'hehehe',(object,), {})))
return type.__new__(cls, 'hehehe',(object,), {}) # 'name' 直接传入了
def __init__(cls, *args):
'''
# 这里的init不是self，传入的是__new__类似的，打印print(cls, args)结果如下
1. a = ModelObject()
2. class C(a)
1. <class '__main__.hehehe'> ()
2. <class '__main__.hehehe'> ('C', (<class '__main__.hehehe'>,), {'__module__': '__main__', '__qualname__': 'C', '__init__': <function C.__init__ at 0x000001B83DDC68B8>})
'''
# print(cls, args)
# print('in SetterAwareType __init__')
# return super(SetterAwareType, cls).__init__(cls, *args) # 创建 class C(a) 时候报错 type.__init__() takes 1 or 3 arguments
return super(SetterAwareType, cls).__init__(cls, )
# return type.__init__(cls, *args) # TypeError: type.__init__() takes 1 or 3 arguments
class ModelObject(SetterAwareType):
def test(self):
print('in ModelObject copy')
a = ModelObject() # _init__ 参数 <class '__main__.hehehe'> ()
class C(a): # _init__ 参数 <class '__main__.hehehe'> ('C', (<class '__main__.hehehe'>,), {'__module__': '__main__', '__qualname__': 'C', '__init__': <function C.__init__ at 0x000002445ED868B8>})
pass
print(type(SetterAwareType)) # type 元类
print(type(ModelObject)) # type 元类
print('a', a)
print(type(a)) # a 是class hehehe，属于ModelObject class
b=a()
print('b', b)
print(type(b)) # b 是obj hehehe，属于hehehe class
a.test() # 类中的函数
# b.test() #obj中报错 # AttributeError: 'hehehe' object has no attribute 'test'
c = C()
# c.test() # AttributeError: 'hehehe' object has no attribute 'test'
- new的正确使用【需要移除】
https://stackoverflow.com/questions/59217884/new-method-giving-error-object-new-takes-exactly-one-argument-the-typ
Your code should be something like
class Foo:
def __new__(cls, a, b, *args, **kwargs):
print("Creating Instance")
instance = super(Foo, cls).__new__(cls, *args, **kwargs)
return instance
def __init__(self, a, b, *args, **kwargs):
super().__init__(*args, **kwargs)
self.a = a
self.b = b
This definition removes your new parameters a and b from args before passing it on to whoever is next on the MRO. Likewise for __init__.
