python:元类中新的时间点

fields['key'] = 'value'

class foo(object):
    var1 = 'bar'

    def foobar(self):
        pass

class

1. var1 = 'bar' locals()['var1'] = 'bar'

2. def foobar locals()['var'] = the result of compiling the function

3. locals() __new__ type

4. foo

A.fields A Meta fields

super().fields B super(B).fields

def MakeFields(**fields):
    return fields

class Meta(type):
    def __new__(mcs, name, bases, attr):
        for base in bases:
            if hasattr(base, 'fields'):
                inherited = getattr(base, 'fields')
                try:
                    attr['fields'].update(inherited)
                except KeyError:
                    attr['fields'] = inherited
                except ValueError:
                    pass
        return type.__new__(mcs, name, bases, attr)

class A(metaclass=Meta):
    fields = MakeFields(id='int',name='varchar') 

class B(A):
    fields = MakeFields(count='int')

class C(B):
    pass

class Test(object):
    fields = "asd"

class D(C, Test):
    pass

print C.fields
print D.fields