python错误：‘Model’ object has no attributes 'save'

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最近跟着廖雪峰老师的教程写一个orm，框架写好了开始测试时出现了如下错误：
我的代码时这样的：

import aiomysql
import asyncio

@asyncio.coroutine
def create_pool(loop, **kw):
    #logging.info('create database connection pool...')
	print('create database connection pool...')
	global __pool
	__pool = yield from aiomysql.create_pool(
	host=kw.get('host', 'localhost'),
		port=kw.get('port', 3306),
		user=kw['user'],
		password=kw['password'],
		db=kw['db'],
		charset=kw.get('charset', 'utf8'),
		autocommit=kw.get('autocommit', True),
		maxsize=kw.get('maxsize', 10),
		minsize=kw.get('minsize', 1),
		loop=loop
    )

@asyncio.coroutine
def select(sql, args, size=None):
	global __pool
	with (yield from __pool) as conn:
		cur = yield from conn.cursor(aiomysql.DictCursor)
		yield from cur.execute(sql.replace('?','%s'), args or ())
		if size:
			rs = yield from cur.fetchall(size)
		else:
			rs = yield from cur.fetchall()
		yield from cur.close()
		logging.info('rows returned: %s' % len(rs))
		return rs

@asyncio.coroutine
def execute(sql, args):
	#log(sql)
	with (yield from __pool) as conn:
		try:
			cur = yield from conn.cursor()
			yield from cur.execute(sql.replace('?', '%s'), args)
			affected = cur.rowcount
			yield from cur.close()
		except BaseException as e:
			raise
		return affected

def create_args_string(num):
    L = []
    for n in range(num):
        L.append('?')
    return ', '.join(L)
		
class Field(object):
	
	def __init__(self, name, column_type, primary_key, default):
		self.name = name
		self.column_type = column_type
		self.primary_key = primary_key
		self.default = default
		
	def __str__(self):
		return '<%s, %s, %s>' %(self.__class__.__name__,self.column_type, self.name)

class StringField(Field):

	def __init__(self, name=None, column_type = 'varchar(100)', primary_key = False, default = None):
		super(StringField, self).__init__(name, column_type, primary_key, default)

class IntegerField(Field):
	
	def __init__(self, name=None, column_type = 'bigint', primary_key = False, default = None):
		super(IntegerField, self).__init__(name, column_type, primary_key, default)
		
class ModelMetaclass(type):
	
	def __new__(cls, name, bases, attrs):
		if name == 'Model':
			return type.__new__(cls, name, bases, attrs)
		tableName = attrs.get('__table__', None) or name
		print('found model: %s(table:%s)' % (name, tableName))
		#获取所有Field和主键名
		mappings = dict()
		fields = []
		primaryKey = None
		for k,v in attrs.items():
			if isinstance(v,Field):
				print('founding mapping:%s ==> %s'%(k,v))
				mappings[k] = v
				if v.primary_key:
					#找到主键
					if primaryKey:
						#主键不能重复
						raise RuntimeError('Duplicate primary key for field:%s' %k)
					primaryKey = k
				else:
					fields.append(k)
		if not primaryKey:
			raise RuntimeError('primaryKey not found')
		for k in mappings.keys():
			attrs.pop(k)
		escaped_fields = list(map(lambda f:'%s' %f, fields))
		attrs['__mappings__'] = mappings
		attrs['__table__'] = tableName
		attrs['__primary_key__'] = primaryKey #主属性名
		attrs['__fields__'] = fields #除主键外的属性名
		attrs['__select__'] = 'select `%s`, %s from `%s`' % (primaryKey, ', '.join(escaped_fields), tableName)
		attrs['__insert__'] = 'insert into `%s` (%s, `%s`) values (%s)' % (tableName, ', '.join(escaped_fields), primaryKey, create_args_string(len(escaped_fields) + 1))
		attrs['__update__'] = 'update `%s` set %s where `%s`=?' % (tableName, ', '.join(map(lambda f: '`%s`=?' % (mappings.get(f).name or f), fields)), primaryKey)
		attrs['__delete__'] = 'delete from `%s` where `%s`=?' % (tableName, primaryKey)
		return type.__new__(cls, name, bases, attrs)
		
class Model(dict, metaclass=ModelMetaclass):
	
	def __init__(self, **kw):
		super(Model, self).__init__(**kw)

	def __getattr__(self, key):
		try:
			return self[key]
		except KeyError:
			raise AttributeError(r"'Model' object has no attribute '%s'" % key)

	def __setattr__(self, key, value):
		self[key] = value

	def getValue(self, key):
		return getattr(self, key, None)

	def getValueOrDefault(self, key):
		value = getattr(self, key, None)
		if value is None:
			field = self.__mappings[key]
			if field.default is not None:
				value = field.default() if callable(field.default) else field.default
				logging.debug('using default value for %s:%s'%(key, str(value)))
				setattr(self, key, value)
		return value
	
	@classmethod
	async def find(cls, pk):
		'find object by primaryKey'
		rs = await select('%s where %s = ?' % (cls.__select__, cls.__primary_key__), [pk], 1)
		if len(rs) == 0:
			return None
		return cls(**rs[0])

	@classmethod
	async def save(self):
		args = list(map(self.getValueOrDefault, self.__fields__))
		args.append(self.getValueOrDefault(self.__primary_key__))
		rows = await execute(self.__insert__, args)
		print(rows)
		if rows != 1:
			logging.warn('failed to insert record:affected rows:%s'%rows)

class User(Model):
	__table__ = 'user'
	
	id = IntegerField(primary_key = True)
	name = StringField()

@asyncio.coroutine
def destory_pool():
	global __pool
	if __pool is not None:
		__pool.close()
		yield from __pool.wait_closed()

@asyncio.coroutine	
def test():
	yield from create_pool(loop,user = 'root',password = 'zxzx',db = 'orm_test',host = '127.0.0.1')
	u = User(id = 334, name = 'zxlw')
	yield from u.sava()
	yield from destory_pool()
	

loop = asyncio.get_event_loop()
loop.run_until_complete(test())
loop.close()

这个代码基本参照廖老师的代码写的，但是我用廖老师github上的代码测试不会出错，希望各位指导一下