code: def add(self, registry):
          
          # POST
          payload = self.formatter.marshall(registry)
          r = requests.post(self.path, data=payload, headers=self.headers)
docs: Add works like replace, but only previously pushed metrics with the
              same name (and the same job and instance) will be replaced.
              (It uses HTTP method 'POST' to push to the Pushgateway.)