How do I organize this code?

Question

I'm trying to sort functions into their appropriate classes by turning them into methods (it is possible to leave a function outside of the class if it seems appropriate). But I'm not sure what to do with this particular function (shown below).

First, here is my class:

class OreBlobAction:
   def __init__(self, entity, image_store):
      self.entity = entity
      self.image_store = image_store

   def ore_blob_action(self, world, action, ticks):
      entity = self.entity
      entity_pt = entities.get_position(self.entity)
      vein = find_nearest(world, entity_pt, entities.Vein)
      (tiles, found) = blob_to_vein(world, self.entity, vein)

      next_time = ticks + entities.get_rate(entity)
      if found:
         quake = create_quake(world, tiles[0], ticks, self.image_store)
         worldmodel.add_entity(world, quake)
         next_time = ticks + entities.get_rate(entity) * 2

      schedule_action(world, self.entity,
         OreBlobAction(self.entity, self.image_store), next_time)

      return tiles

And now, here is the function:

def take_action(world, action, ticks):
   entities.remove_pending_action(action.entity, action)
   if isinstance(action, VeinAction):
      return vein_action(world, action, ticks)
   elif isinstance(action, MinerNotFullAction):
      return miner_not_full_action(world, action, ticks)
   elif isinstance(action, MinerFullAction):
      return miner_full_action(world, action, ticks)
   elif isinstance(action, OreBlobAction):
      return ore_blob_action(world, action, ticks)
   elif isinstance(action, OreTransformAction):
      return ore_transform_action(world, action, ticks)
   elif isinstance(action, EntityDeathAction):
      return entity_death_action(world, action, ticks)
   elif isinstance(action, WyvernSpawnAction):
      return wyvern_spawn_action(world, action, ticks)
   elif isinstance(action, WyvernAction):
      return wyvern_action(world, action, ticks)
   elif isinstance(action, VeinSpawnAction):
      return vein_spawn_action(world, action, ticks)
   elif isinstance(action, AnimationAction):
      return animation_action(world, action, ticks)

   return []

As you can see, this function accounts for the actions of not only the OreBlobAction class, but also multiple others. Would it be better to leave this function outside of the OreBlobAction class? Or is there a better way to do this?

NOTE: If I leave this function out of the OreBlobAction class, and I try to run the program, I get this error:

NameError: global name 'ore_blob_action' is not defined

Answer 1

Your big switch statement on the type of the action is a red flag for refactoring. Is there anything to stop you moving the "take action" method into the action class itself? For instance

class Action(object):
    """ An action that can be performed on the game world. """

    def perform(self, world, ticks):
        """ Perform the action. """
        raise NotImplementedError()

This would be your base action class, then within each type of action, you would override the perform(...) method, for example

class WyvernSpawnAction(Action):
    """ An action that spawns a Wyvern. """

    [... Some action specific initialisation code here ...]

    def perform(self, world, ticks):
        """ Spawn a Wyvern. """
        world.spawn(Wyvern(...))

Your boilerplate to remove the action from the world would remain, and you can now freely add new types of action without eventually adding hundreds more comparisons within your function. In addition, you can now handle cases where actions can inherit the behaviour of other actions without having to be extremely careful about the ordering of your comparisons.