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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 comment_thread(cls, backend, *args, **kwargs):
 """Create a comment thread for the desired backend. :arg backend: String name of backend (e.g., 'file', 'github', 'redis', etc.). :arg *args, **kwargs: Arguments to be passed to contructor for that backend. ~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~- :returns: A CommentThread sub-class for the given backend. ~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~-~- PURPOSE: Some simple syntatic sugar for creating the desired backend. """

        ct_cls = cls._known_backends.get(backend)
        if not ct_cls:
            return None
        return ct_cls(*args, **kwargs)