code: def exists(self, key, **opts):
          
          key, store = self._expand_opts(key, opts)
          data = store.get(key)
          # Note that we do not actually delete the thing here as the max_age
          # just for this call may have triggered a False.
          if not data or self._has_expired(data, opts):
              return False
          return True
docs: Return if a key exists in the cache.