code: def create_dummy_func(func, dependency):
      
      assert not building_rtfd()
  
      if isinstance(dependency, (list, tuple)):
          dependency = ','.join(dependency)
  
      def _dummy(*args, **kwargs):
          raise ImportError("Cannot import '{}', therefore '{}' is not available".format(dependency, func))
      return _dummy
docs: When a dependency of a function is not available, create a dummy function which throws ImportError when used.
  
      Args:
          func (str): name of the function.
          dependency (str or list[str]): name(s) of the dependency.
  
      Returns:
          function: a function object