Python 用_getattr___和相关

我试图封装一个对象而不改变它的默认行为，问题是当我访问该对象时，它已经被构造好了。因此，我的想法是使用继承并使用

\uuuu getattr\uuuuuu

、

\uuuu setattr\uuuuuu

、

\uuuu getitem\uuuuuu

和

\uuuu setitem\uuuuuuuuuuuu

并委托给封装对象，但我自己定义的字段除外

class Request(HttpRequest):

    def __init__(self, request, *args, **kwargs):
        self._original_request = request
        super(Request, self).__init__(*args, **kwargs)

    def __getattr__(self, name):
        return getattr(self._original_request, name)

    def __setattr__(self, name, value):
        if name == '_original_request':
            super(Request, self).__setattr__(name, value)
        else:
            self._original_request.__setattr__(name, value)

    def __getitem__(self, key):
        return self._original_request[key]

    def __setitem__(self, key, value):
        self._original_request[key] = value

如果我沿着原始对象传递，一切都很好。如果我不这样做，我就会

host = self.META['SERVER_NAME']
KeyError: u'SERVER_NAME'

我错过什么了吗？我的类不应该和它封装的类完全一样吗

Internal Server Error: /
Traceback (most recent call last):
  File "c:\Python27\lib\site-packages\django\core\handlers\base.py", line 115, in get_response
    response = callback(request, *callback_args, **callback_kwargs)
  File "c:\Python27\lib\site-packages\django\views\generic\base.py", line 68, in view
    return self.dispatch(request, *args, **kwargs)
  File "C:\www\lookwanted\djutils\views.py", line 35, in dispatch
    return super(View, self).dispatch(Request(request), *args, **kwargs)
  File "C:\www\lookwanted\djutils\views.py", line 12, in __init__
    super(Request, self).__init__(*args, **kwargs)
  File "c:\Python27\lib\site-packages\django\http\request.py", line 43, in __init__
    self.GET, self.POST, self.COOKIES, self.META, self.FILES = {}, {}, {}, {}, {}
  File "C:\www\lookwanted\djutils\views.py", line 21, in __setattr__
    self._original_request.__setattr__(name, value)
AttributeError: can't set attribute
Traceback (most recent call last):
  File "c:\Python27\lib\wsgiref\handlers.py", line 85, in run
    self.result = application(self.environ, self.start_response)
  File "c:\Python27\lib\site-packages\django\contrib\staticfiles\handlers.py", line 72, in __call__
    return self.application(environ, start_response)
  File "c:\Python27\lib\site-packages\django\core\handlers\wsgi.py", line 255, in __call__
    response = self.get_response(request)
  File "c:\Python27\lib\site-packages\django\core\handlers\base.py", line 178, in get_response
    response = self.handle_uncaught_exception(request, resolver, sys.exc_info())
  File "c:\Python27\lib\site-packages\django\core\handlers\base.py", line 217, in handle_uncaught_exception
    return debug.technical_500_response(request, *exc_info)
  File "c:\Python27\lib\site-packages\django\views\debug.py", line 69, in technical_500_response
    html = reporter.get_traceback_html()
  File "c:\Python27\lib\site-packages\django\views\debug.py", line 298, in get_traceback_html
    return t.render(c)
  File "c:\Python27\lib\site-packages\django\template\base.py", line 140, in render
    return self._render(context)
  File "c:\Python27\lib\site-packages\django\template\base.py", line 134, in _render
    return self.nodelist.render(context)
  File "c:\Python27\lib\site-packages\django\template\base.py", line 830, in render
    bit = self.render_node(node, context)
  File "c:\Python27\lib\site-packages\django\template\debug.py", line 74, in render_node
    return node.render(context)
  File "c:\Python27\lib\site-packages\django\template\defaulttags.py", line 284, in render
    return nodelist.render(context)
  File "c:\Python27\lib\site-packages\django\template\base.py", line 830, in render
    bit = self.render_node(node, context)
  File "c:\Python27\lib\site-packages\django\template\debug.py", line 74, in render_node
    return node.render(context)
  File "c:\Python27\lib\site-packages\django\template\debug.py", line 84, in render
    output = self.filter_expression.resolve(context)
  File "c:\Python27\lib\site-packages\django\template\base.py", line 578, in resolve
    obj = self.var.resolve(context)
  File "c:\Python27\lib\site-packages\django\template\base.py", line 728, in resolve
    value = self._resolve_lookup(context)
  File "c:\Python27\lib\site-packages\django\template\base.py", line 779, in _resolve_lookup
    current = current()
  File "c:\Python27\lib\site-packages\django\http\request.py", line 112, in build_absolute_uri
    self.get_host(), self.path)
  File "c:\Python27\lib\site-packages\django\http\request.py", line 62, in get_host
    host = self.META['SERVER_NAME']
KeyError: u'SERVER_NAME'

---

堆栈跟踪显示了问题：代码试图在

self.\u原始\u请求

上设置属性，而不是

self.\uuuu dict\uuuu

---

请阅读Python文档。

问题在于行：

    super(Request, self).__init__(*args, **kwargs)

这将导致对您的

请求

实例调用

HttpRequest

类的

\uuuuuu init\uuuu

方法，这是没有意义的。因此，只要摆脱这一行

另外，我不明白你为什么要在第一时间子类化。既然python有duck类型，并且您完全包装了内部对象，为什么不使用：

class Request(object):
    def __init__(self, request, *args, **kwargs):
        self._original_request = request

    def __getattr__(self, name):
        return getattr(self._original_request, name)

    def __setattr__(self, name, value):
        if name == '_original_request':
            super(Request, self).__setattr__(name, value)
        else:
            self._original_request.__setattr__(name, value)

    def __getitem__(self, key):
        return self._original_request[key]

    def __setitem__(self, key, value):
        self._original_request[key] = value

---

你能发布完整的回溯吗？另外，为什么要继承

HttpRequest

？这样做时，我注意到还有一个我没有注意到的异常。。。我将super（Request，self）改为setattr（name，value），但现在我得到了无限递归。不过，我想这是另一个问题。当然不是你的问题，但我真的不明白这句话的意思是什么。你为什么不直接写一句话呢！由于

META

是

HttpRequest

的一个属性，通过对其进行子分类，您的“拦截器”将获得其自己的

META

属性，因此，

\uuu getattr\uuuu

不会被触发。。。因此没有访问原始对象的

META

属性。我明白了！接得好！关于遗产，它会造成伤害吗？我正在考虑让它保持原样，如果没有其他原因，它记录了这两个类是相关的。事实上，这是一个有趣的评论。因为这是python，所以不需要使用子类型来获得可替换性——这需要Java等语言的接口。所以这里有某种继承感。另一方面，请求对象“不是”传统Java继承意义上的HttpRequest对象，在这种继承中，构造子类型需要通过构造函数调用构造超类型。就我个人而言，我会避免这样做，但我不认为有一个最好的方法来做这件事。