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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 list_all_files(self):
 """ Utility method that yields all files on the device's file systems. """

        def list_files_recursively(directory):
            f_gen = itertools.chain(
                directory.files,
                *tuple(list_files_recursively(d)
                       for d in directory.directories))
            for f in f_gen:
                yield f
        return list_files_recursively(self.filesystem)