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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 extra(name: str, desc: str) -> Callable: """ Decorator for slave channel's "additional features" interface. Args: name (str):
 A human readable name for the function. desc (str):
 A short description and usage of it. Use ``{function_name}`` in place of the function name in the description. Returns: The decorated method. """


    def attr_dec(f):
        f.__setattr__("extra_fn", True)
        f.__setattr__("name", name)
        f.__setattr__("desc", desc)
        return f

    return attr_dec