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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 subst_src_suffixes(self, env):
 """ The suffix list may contain construction variable expansions, so we have to evaluate the individual strings. To avoid doing this over and over, we memoize the results for each construction environment. """

        memo_key = id(env)
        try:
            memo_dict = self._memo['subst_src_suffixes']
        except KeyError:
            memo_dict = {}
            self._memo['subst_src_suffixes'] = memo_dict
        else:
            try:
                return memo_dict[memo_key]
            except KeyError:
                pass
        suffixes = [env.subst(x) for x in self.src_suffix]
        memo_dict[memo_key] = suffixes
        return suffixes