docs: def instance_variables(self):
          """
          Returns all instance variables in the class, sorted
          alphabetically as a list of `pydoc.Variable`. Instance variables
          are attributes of `self` defined in a class's `__init__`
          method.
          """
          p = lambda o: isinstance(o, Variable) and self.module._docfilter(o)
          return filter(p, self.doc_init.values())