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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 _ass_needs_refresh(self, cached_ass, file_ass):
 """Checks if assistant needs refresh. Assistant needs refresh iff any of following conditions is True: - stored source file is different than given source file - stored assistant ctime is lower than current source file ctime - stored list of subassistants is different than given list of subassistants - stored ctime of any of the snippets that this assistant uses to compose args is lower than current ctime of that snippet Args: cached_ass: an assistant from cache hierarchy (for format see Cache class docstring) file_ass: the respective assistant from filesystem hierarchy (for format see what refresh_role accepts) """

        if cached_ass['source'] != file_ass['source']:
            return True
        if os.path.getctime(file_ass['source']) > cached_ass.get('ctime', 0.0):
            return True
        if set(cached_ass['subhierarchy'].keys()) != set(set(file_ass['subhierarchy'].keys())):
            return True
        for snip_name, snip_ctime in cached_ass['snippets'].items():
            if self._get_snippet_ctime(snip_name) > snip_ctime:
                return True

        return False