docs: def clear_instance_cache(cls, func):
          """ clear the instance cache
  
          Decorate a method of a class, the first parameter is
          supposed to be `self`.
          It clear all items cached by the `instance_cache` decorator.
          :param func: function to decorate
          """
  
          @functools.wraps(func)
          def func_wrapper(*args, **kwargs):
              if not args:
                  raise ValueError('`self` is not available.')
              else:
                  the_self = args[0]
  
              cls.clear_self_cache(the_self)
              return func(*args, **kwargs)
  
          return func_wrapper