docs: def get_keys_for(self, value):
          """Get keys for a given value.
  
          :param value: The value to look for
          :type value: object
          :return: The keys for the given value
          :rtype: list(str)
  
          """
          if callable(value):
              return value(self)
          hash_value = self.get_hash_for(value)
          return self._index[hash_value][:]