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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 _new_ass_hierarchy(self, file_ass):
 """Returns a completely new cache hierarchy for given assistant file. Args: file_ass: the assistant from filesystem hierarchy to create cache hierarchy for (for format see what refresh_role accepts) Returns: the newly created cache hierarchy """

        ret_struct = {'source': '',
                      'subhierarchy': {},
                      'attrs': {},
                      'snippets': {}}
        ret_struct['source'] = file_ass['source']
        self._ass_refresh_attrs(ret_struct, file_ass)

        for name, subhierarchy in file_ass['subhierarchy'].items():
            ret_struct['subhierarchy'][name] = self._new_ass_hierarchy(subhierarchy)

        return ret_struct