class LowerAttrMetaClass_4(type):
def __new__(cls, name, bases, dct):
attrs = ((name, value) for name, value in dct.items() if not name.startswith('__'))
lowercase_attr = dict((name.lower(), value) for name, value in attrs)
return super(LowerAttrMetaClass_4, cls).__new__(cls, name, bases, lowercase_attr)
class MetaClassTest(object, metaclass=LowerAttrMetaClass_4):
Say = "hello world"
def __init__(self, name, age):
super(MetaClassTest, self).__init__()
self.name = name
self.age = age
def Run(self):
print("MetaClassTest run method")
tmp_obj = MetaClassTest(name="zzz", age=20)
执行如上代码，总是报如下错误：
DeprecationWarning: class not set defining 'MetaClassTest' as . Was classcell propagated to type.new?
class MetaClassTest(object, metaclass=LowerAttrMetaClass_4):
Traceback (most recent call last):
File "E:/zzz/meta.py", line 286, in
tmp_obj = MetaClassTest(name="zzz", age=20)
TypeError: MetaClassTest() takes no arguments
请教：
（1）为什么会报 DeprecationWarning？
（2）为什么会报 MetaClassTest() takes no arguments，我明明传了参数进去的呀？
class LowerAttrMetaClass_4(type):
def new(cls, name, bases, dct):
lowercase_attr = {}
for name, val in dct.items():
if name.startswith(''):
lowercase_attr[name] = val
else:
lowercase_attr[name.lower()] = val
return super(LowerAttrMetaClass_4, cls).new__(cls, name, bases, lowercase_attr)
class MetaClassTest(metaclass=LowerAttrMetaClass_4):
Say = "hello world"
def init(self, name, age):
super(MetaClassTest, self).init()
self.name = name
self.age = age
def Run(self):
print("MetaClassTest run method")
tmp_obj = MetaClassTest(name="zzz", age=20)
修改成这样就可以了。你错误的原因是 attrs = ((name, value) for name, value in dct.items() if not name.startswith(''))，把类里的其他属性都干掉了，这个开头的类属性都没有了
同楼上，楼主在避免处理魔术方法时把带__的方法都漏掉了，漏掉了__classcell__，所以报 DeprecationWarning，高版本 python 应该会报 RuntimeError，漏掉了__init__，类创建后默认使用了无参初始化方法，所以报 MetaClassTest() takes no arguments
class LowerAttrMetaClass_4(type):
def __new__(mcs, name, bases, attr):
attr = {key if key[:2] == "__" else key.lower(): value for key, value in attr.items()}
return type.__new__(mcs, name, bases, attr)
class MetaClassTest(metaclass=LowerAttrMetaClass_4):
Say = "hello world"
def __init__(self, name, age):
self.name = name
self.age = age
def Run(self):
print("MetaClassTest run method")
tmp_obj = MetaClassTest(name="zzz", age=20)
tmp_obj.run()
# >>>
# MetaClassTest run method