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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 filter(self, search):
 """ Add a ``post_filter`` to the search request narrowing the results based on the facet filters. """

        if not self._filters:
            return search

        post_filter = MatchAll()
        for f in itervalues(self._filters):
            post_filter &= f
        return search.post_filter(post_filter)