ValueError: cannot switch from manual field specification to automatic field numbering

附源码：

class SingletonObject(object):
    class __SingletonObject():
        def __init__(self):
            print ('init')
            self.val=None

        def __str__(self):
            # print ('str' )
            return "{0!r} {}".format(self,self.val)

    instance = None

    def __new__(cls):
        if not SingletonObject.instance:
            print( 'set')
            SingletonObject.instance = SingletonObject.__SingletonObject()
        print ('s')
        return SingletonObject.instance

    def __getattr__(self, item):
        print ('hello')
        return getattr(self.instance, item)

    def __setattr__(self, key,value):
        print ('get')
        return setattr(self.instance, value)


obj1 = SingletonObject()
obj1.val = 'value 1'
print("*"*22)
print("print obj1:",obj1)

obj2 = SingletonObject()
obj2.val = 'value 2'
print(obj1)
print(obj2)
print(obj1.val)

错误：

改：