code: def set(cls, var_name: str, value: Any) -> 'Configuration':
          
          with cls._lock:
              if var_name not in cls().cache:
                  cls().cache[var_name] = value
              else:
                  raise ConfigurationError(
                      f'Value for {var_name} already set')
          return cls()
docs: Set the variable
  
          :param var_name: Variable name
          :param value: Value of variable
          :return: :class:`~haps.config.Configuration` instance for easy\
                    chaining