dir（）与uu getattr_uu一起执行什么样的python魔术？

下面是python 2.7和MySQLDB1.2.3中的内容

我需要一个类包装器来为不支持它的对象添加一些属性（带有

\uuuu插槽的类和/或一些用C编写的类），所以我得出了如下结论：

class Wrapper(object):

    def __init__(self, obj):
        self._wrapped_obj = obj

    def __getattr__(self, obj):
        return getattr(self._wrapped_obj, attr)

我原以为对我的
Wrapper
实例调用的
dir（）
内置函数应该只返回object plus
wrapped\u obj
继承的名称，我发现大多数情况下都是这样，但并非所有情况都是这样。我用一个定制的旧样式类、一个定制的新样式类和一些内置类尝试了这一点，它总是这样工作：我发现的唯一例外是当包装对象是类的实例时
\u mysql.connection
。在本例中，我的对象上的
dir（）
碰巧也知道附加到包装连接对象的所有方法名

我在python文档中读到了关于
dir
，这种行为似乎是合法的：
dir
应该返回一个“有趣的名称”列表，而不是实例的“真实”内容。但我真的不明白它是如何做到这一点的：它实际上理解我的
\uuu getattr\uuuu
的实现，并解析为附加项？如果这是真的，为什么只使用该
连接
类，而不使用更简单的
dict

下面是一些粘贴的代码，作为这种奇怪行为的示例：

>>> from _mysql import connection
>>> c = connection(**connection_parameters)
>>> c
<_mysql.connection open to '127.0.0.1' at a16920>
>>> 
>>> dir(c)
['affected_rows', 'autocommit', 'change_user', 'character_set_name', 'close', 'commit', 'dump_debug_info', 'errno', 'error', 'escape', 'escape_string', 'field_count', 'get_character_set_info', 'get_host_info', 'get_proto_info', 'get_server_info', 'info', 'insert_id', 'kill', 'next_result', 'ping', 'query', 'rollback', 'select_db', 'set_character_set', 'set_server_option', 'shutdown', 'sqlstate', 'stat', 'store_result', 'string_literal', 'thread_id', 'use_result', 'warning_count']
>>> 
>>> w = Wrapper(c)
>>> dir(w)
['__class__', '__delattr__', '__dict__', '__doc__', '__format__', '__getattr__', '__getattribute__', '__hash__', '__init__', '__module__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '__weakref__', '_wrapped_obj', 'affected_rows', 'autocommit', 'change_user', 'character_set_name', 'close', 'commit', 'dump_debug_info', 'errno', 'error', 'escape', 'escape_string', 'field_count', 'get_character_set_info', 'get_host_info', 'get_proto_info', 'get_server_info', 'info', 'insert_id', 'kill', 'next_result', 'ping', 'query', 'rollback', 'select_db', 'set_character_set', 'set_server_option', 'shutdown', 'sqlstate', 'stat', 'store_result', 'string_literal', 'thread_id', 'use_result', 'warning_count']
>>> 
>>> d = Wrapper({})
>>> dir(d)
['__class__', '__delattr__', '__dict__', '__doc__', '__format__', '__getattr__', '__getattribute__', '__hash__', '__init__', '__module__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '__weakref__', '_wrapped_obj']
>>> 

来自mysql导入连接的
>>
>>>c=连接（**连接参数）
>>>c
>>> 
>>>处长（c）
[‘受影响的行’、‘自动提交’、‘更改用户’、‘字符集名称’、‘关闭’、‘提交’、‘转储调试信息’、‘错误’、‘转义’、‘转义字符串’、‘字段计数’、‘获取字符集信息’、‘获取主机信息’、‘获取协议信息’、‘获取服务器信息’、‘插入id’、‘杀死’、‘下一个结果’、‘ping’、‘查询’、‘回滚’、‘选择数据库’、‘设置字符’et“，”设置服务器选项“，”关机“，”sqlstate“，”统计“，”存储结果“，”字符串文字“，”线程id“，”使用结果“，”警告计数“]
>>> 
>>>w=包装器（c）
>>>署长（西）
“UUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUU，”UUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUU","大小","str","子类钩子","weakref","包装对象","受影响行","自动提交","更改用户","字符集"名称"“，”关闭“，”提交“，”转储调试信息“，”错误“，”转义“，”转义字符串“，”字段计数“，”获取字符集信息“，”获取主机信息“，”获取协议信息“，”获取服务器信息“，”信息“，”插入id“，”杀死“，”下一个结果“，”ping“，”查询“，”回滚“，”选择数据库“，”设置字符集“，”设置服务器选项“，”关机“，”sqlstate“，”存储“，”esult'，string\u literal'，thread\u id'，use\u result'，warning\u count']
>>> 
>>>d=包装器（{}）
>>>署长（丁）
“UUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUU，”UUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUU","大小","str","子类钩子","weakref","包装"obj"
>>> 
Python 2中有两个不推荐使用的属性；它们旨在支持扩展类型（C定义的对象）上的
dir（）
：

对象。方法
自版本2.2以来已弃用：使用内置函数
dir（）
获取对象属性的列表。此属性不再可用

对象。\uuuu成员\uuuu


自版本2.2以来已弃用：使用内置函数dir（）获取对象属性的列表。此属性不再可用

这些属性已从Python 3中删除，但这是因为您的连接对象（至少在您使用的旧版本中）仍然提供了一个
\uuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuu方法
属性，该属性可通过
\uuuuuuuuuuuuuuu

如果将
print
语句添加到
\uuu getattr\uuu
方法中，您将看到正在访问的属性：

>>> class Wrapper(object):
...     def __init__(self, obj):
...         self._wrapped_obj = obj
...     def __getattr__(self, obj):
...         print 'getattr', obj
...         return getattr(self._wrapped_obj, attr)
... 
>>> dir(Wrapper({}))
getattr __members__
getattr __methods__
['__class__', '__delattr__', '__dict__', '__doc__', '__format__', '__getattr__', '__getattribute__', '__hash__', '__init__', '__module__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '__weakref__', '_wrapped_obj']

对于新样式的对象，
dir（）
支持的较新样式仅在类型上正确查找，因此您不会看到在此处访问该类型

这表明在1.2.4 beta 1的大型Python 3兼容性更新中删除了这些属性。
我无法真实再现您在Python 2.7和MySQLdb上看到的内容
dir（w）
不包括
c
中的名称。您确定没有在包装器上包含返回
dir（self.\u wrapped\u obj）
的
方法吗？是的，我使用包装器类测试了粘贴的输出，就像上面定义的那样
导入什么；打印mysql.version\u info
生成？
（1,2,3，'final'，0）