__init__和__new__

# 由type创建元类，必须要继承type
class MetaClassFoo(type):

    # 由元类创建类也遵循 名字；继承；方法
    def __new__(cls, name, base, attrs):
        # 天赋，赋予给通过该元类创建的类
        attrs[‘func‘] = lambda self: ‘im %s and i have func!‘ % self.name
        return type.__new__(cls, name, base, attrs)


# 由元类创建类
class Foo(object):

    __metaclass__ = MetaClassFoo

    def __init__(self):
        self.name = ‘www‘


# 由类创建实例，并生成方法
print Foo().func()

class SingleObj(object):
    def __new__(cls):
        # 关键在于这，每一次实例化的时候，我们都只会返回这同一个instance对象
        if not hasattr(cls, ‘instance‘):
            cls.instance = super(SingleObj, cls).__new__(cls)  # 使用__new__最好返回super()方法
        return cls


obj1 = SingleObj()
obj2 = SingleObj()

obj1.attr1 = ‘value1‘
print obj1.attr1, obj2.attr1
print obj1 is obj2

# out:
value1 value1
True