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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 process_response(self, request, response):
 """ Forces the HTTP ``Vary`` header onto requests to avoid having responses cached across subdomains. """

        if getattr(settings, 'FORCE_VARY_ON_HOST', True):
            patch_vary_headers(response, ('Host',))

        return response