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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 __sub_del_reference(self, req, key):
 """Blindly clear reference to pending subscription on failure."""

        if not req.success:
            try:
                self.__new_subs.pop(key)
            except KeyError:
                logger.warning('No sub ref %s', key)