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.

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())