old_contents: from six import string_types
  
  from django.db.models import signals
  
  from .invalidation import invalidate_paths
  
  
  def register(model):
      register_instance_function_at_save(model, invalidate_model_paths)
  
  
  def register_instance_function_at_save(model, function):
  
      def save_function(sender, instance, **kwargs):
          function(instance)
  
      signals.post_save.connect(save_function, model, weak=False)
      signals.pre_delete.connect(save_function, model, weak=False)
  
  
  def get_paths_from_model(model):
      paths = model.dependent_paths()
      if isinstance(paths, string_types):
          model_name = model.__class__.__name__
          raise TypeError(
              ('dependent_paths on {} should return a list of paths, not a'
               'string'.format(model_name))
          )
      return paths
  
  
  def invalidate_model_paths(model):
      paths = get_paths_from_model(model)
      invalidate_paths(paths)
  
new_contents: from six import string_types
  
  from django.db.models import signals
  
  from .invalidation import invalidate_paths
  
  
  def register(model):
      register_instance_function_at_save(model, invalidate_model_paths)
  
  
  def register_instance_function_at_save(model, function):
  
      def save_function(sender, instance, **kwargs):
          function(instance)
  
      signals.post_save.connect(save_function, model, weak=False)
      signals.pre_delete.connect(save_function, model, weak=False)
  
  
  def get_paths_from_model(model):
      paths = model.dependent_paths()
      if isinstance(paths, string_types):
          model_name = model.__class__.__name__
          raise TypeError(
              ('dependent_paths on {model_name} should return a list of paths, '
               ' not a string'.format(model_name=model_name))
          )
      return paths
  
  
  def invalidate_model_paths(model):
      paths = get_paths_from_model(model)
      invalidate_paths(paths)
  
subject: Use keyword based `format` to maintain 2.6 compatibility