python metaclass的理解

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python metaclass的理解
1.type,获得变量类型 type(object) -> the object’s type

>>> a = 2>>> type(a)<type 'int'>>>> type(type(a))<type 'type'>>>>>>> class MM(object):...    def __init__(self):...       self.a = a... >>> mm = MM()>>> type(mm)<class '__main__.MM'>>>> isinstance(mm,MM)True>>> >>>> type(MM)<type 'type'>>>>

type 生成类 type(name, bases, dict) -> a new type

>>> def func(self):...    print "self.a is ",self.a... >>> MyClass = type('MyClass',(object,),{'func':func,'a':100})>>> myclass = MyClass()>>> myclass.func()self.a is  100>>>

元类,任何一个类建立的时候都需要元类来创建，元类可以用来改变类
比如下面这个元类就是将类中的变量名改成小写

class UpdateMetaClass(type):    def __new__(cls,name,bases,attrslist):        attrs = ((name,value) for name,value in attrslist.items() if not name.startswith("__"))        lower_attrs = dict((name.lower(),value) for name,value in attrs)        #return type.__new__(cls,name,bases,lower_attrs)        return super(UpdateMetaClass,cls).__new__(cls,name,bases,lower_attrs)class MyClassTest(object):    __metaclass__ = UpdateMetaClass    AA = 1000#AA has been changed to be aaprint MyClassTest.aa

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