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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def descendents(self, cls):
 """ Returns a descendent list of documentation objects for `cls`, which must be a documentation object. The list will contain objects belonging to `pydoc.Class` or `pydoc.External`. Objects belonging to the former are exported classes either in this module or in one of its sub-modules. """

        if cls.cls == type or not hasattr(cls.cls, '__subclasses__'):
            # Is this right?
            return []

        downs = cls.cls.__subclasses__()
        return list(map(lambda c: self.find_class(c), downs))