Python 3.5类型提示动态生成的实例属性

Question

我想为动态生成的对象属性添加Python 3.5类型提示，以便IDE正确地自动完成它们。这里的“动态”是指在类创建过程中或在__init__或任何其他方法中不存在该属性。

例如。有没有办法通过评论或其他技巧添加这些？如果不是，我可以回退添加虚拟类属性。

例：：

 class Request:
      """Example HTTP request object.

      We have `get_user()`  but we do not declare it anyhere.
      """

 ...


 # Pyramid's way of plugging in methods and properties to request, enabled addon capabilities for the framework
 # adds Request.user - done in different part of application lifecycle, not during class creation
 config.add_request_method(auth.get_user, 'user', reify=True)

目标是使这项工作能够使PyCharm和其他IDE完成此属性。

Answer 1

在Python 3.6+中，您可以使用类级别类型提示 - 这些提示不会在类中生成属性。即

class Request(_Request):
    user: Optional[User]

这不会在类中创建属性，只会创建注释。

>>> Request.user
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: type object 'Request' has no attribute 'user'

>>> Request.__annotations__
{'user': typing.Union[foo.User, NoneType]}

在Python 3.5中，可以创建一个返回非数据描述符的函数（即没有__set__的描述符）;这将被一个实例属性覆盖，但它带来一些最小的运行时开销 - 描述符将从__dict__获取并检查它是否定义了__set__插槽 - 即使是所有读取。它可能看起来像

class Request(_Request):
    user = typed(User)

其中typed定义为

def typed(type: Type[T]) -> T:
    ... return a dummy non-data-descriptor...

这应该足以让PyCharm正确地推断出类型。

Answer 2

• 我将真正的类分类
• 我在课堂上添加了人造__type_hinting__方法
• 我使用这个类而不是真正的类作为参数类型提示

  class Request(_Request):
      """
      HTTP request class.
      This is a Pyramid Request object augmented with type hinting information for Websauna-specific functionality.
      To know more about request read also
      * py:class:`pyramid.request.Request` documentation
      * py:class:`webob.request.Request` documentation
  
      Counterintuitively, this request is also available in non-HTTP applications like command line applications and timed tasks. 
      These applications do not get request URL from a front end HTTP webserver, but a faux request is constructed pointing to the website URL taken from ``websauna.site_url`` setting. 
      This is to allow similar design patterns and methodology to be applied in HTTP and non-HTTP applications.
  
      By setting variables in ``__type_hinting__()`` based on arguments types allows IDEs to infer type information when you hint your views as::
  
           from websauna.system.http import Request
  
           def hello_world(request: Request):
               request.  # <-- When typing, here autocompletion kicks in.
  
      """
  
      def __type_hinting__(self, user: Optional[User], dbsession: Session, session: ISession, admin: Admin, registry: Registry):
          """
          A dummy helper function to tell IDEs about reify'ed variables.
          :param user: The logged in user. None if the visitor is anonymous.
          :param dbsession: Current active SQLAlchemy session
          :param session: Session data for anonymous and logged in users.
          :param admin: The default admin interface of the site. Note that the site can have several admin interfaces for different purposes.
          :param registry: Pyramid registry's. E.g. 
              :py:attr:`pyramid.registry.Registry.settings` for reading settings and :py:meth:`pyramid.registry.Registry.notify` for sending events.
          """
          self.user = user
          self.dbsession = dbsession
          self.session = session
          self.admin = admin
          self.registry = registry