metaclass_test.py

metaclass_test.py

class MyMetaClass(type):

    def __init__(cls, name, bases, attrs):
        """
        initial class after __new__
        """
        print '__init__ in the metaclass'
        print 'cls:', cls
        print 'name:', name
        print 'bases:', bases
        print 'attrs:', attrs
        r = super(MyMetaClass, cls).__init__(name, bases, attrs)
        print r # r is None
        print '__init__ end\n'
        return r

    def __new__(meta_cls, name, bases, attrs):
        """
        create a new class when define class with 'class statement'
        """
        print '__new__ in the metaclass'
        print 'cls:', meta_cls
        print 'name:', name
        print 'bases:', bases
        print 'attrs:', attrs
        r = super(MyMetaClass, meta_cls).__new__(meta_cls, name, bases, attrs)
        print 'created class:', r
        print '__new__ end\n'
        return r
    
    def __call__(cls, *args, **kwargs):
        """
        create a new instance when call MyClass()
        """
        print '__call__ in the metaclass'
        print 'cls:', cls
        print 'args:', args
        print 'kwargs:', kwargs
        try:
            return cls.__instance
        except AttributeError:
            cls.__instance = super(MyMetaClass, cls).__call__(*args, **kwargs)
        print 'created instance:', cls.__instance
        print '__call__ end \n'
        return cls.__instance


class Test(object):
    __metaclass__ = MyMetaClass

    def __new__(cls, *args, **kwargs):
        print '__new__ in the Test'
        print 'cls:', cls
        print 'args:', args
        print 'kwargs:', kwargs
        ins = super(Test, cls).__new__(cls, *args, **kwargs)
        print 'created instance:', ins
        print '__new__ end\n'
        return ins

    def __init__(self, *args, **kwargs):
        print '__init__ in the Test'
        print 'self:', self
        print 'args:', args
        print 'kwargs:', kwargs
        print '__init__ end \n'


t1 = Test(1, 2, 3)
t2= Test(3, 4, 5)

print 't1 is t2: ', t1 is t2