evennia/docs/source/Howtos/Tutorial-NPC-Reacting.md

NPCs reacting to your presence

> north 
------------------------------------
Meadow
You are standing in a green meadow. 
A bandit is here. 
------------------------------------
Bandit gives you a menacing look!

This tutorial shows the implementation of an NPC object that responds to characters entering their location.

What we will need is the following:

• An NPC typeclass that can react when someone enters.
• A custom Room typeclass that can tell the NPC that someone entered.
• We will also tweak our default Character typeclass a little.

# in mygame/typeclasses/npcs.py  (for example)

from typeclasses.characters import Character

class NPC(Character):
    """
    A NPC typeclass which extends the character class.
    """
    def at_char_entered(self, character, **kwargs):
        """
        A simple is_aggressive check.
        Can be expanded upon later.
        """
        if self.db.is_aggressive:
            self.execute_cmd(f"say Graaah! Die, {character}!")
        else:
            self.execute_cmd(f"say Greetings, {character}!")

Note that we don't use the `**kwargs` property here. This can be used to pass extra information into hooks in your game and would be used when you make custom move commands. For example, if you `run` into the room, you could inform all hooks by doing `obj.move_to(..., running=True)`. Maybe your librarian NPC should have a separate reaction for people running into their library!

We make sure to pass the `**kwargs` from the standard `at_object_receive` hook below.

Here we make a simple method on the NPC˙ called at_char_entered. We expect it to be called when a (player-)character enters the room. We don't actually set the is_aggressive Attribute beforehand; we leave this up for the admin to activate in-game. if it's not set, the NPC is simply non-hostile.

Whenever something enters the Room, its at_object_receive hook will be called. So we should override it.

# in mygame/typeclasses/rooms.py

from evennia import utils

# ... 

class Room(ObjectParent, DefaultRoom):

    # ... 
    
    def at_object_receive(self, arriving_obj, source_location, **kwargs):
        if arriving_obj.account: 
            # this has an active acccount - a player character
            for item in self.contents:
                # get all npcs in the room and inform them
                if utils.inherits_from(item, "typeclasses.npcs.NPC"):
                    item.at_char_entered(arriving_obj, **kwargs)

Remember that Rooms are `Objects`, and other Objects have these same hooks. So an `at_object_receive` hook will fire for you when you pick something up (making you 'receive' it). Or for a box when putting something inside it, for example.

A currently puppeted Character will have an .account attached to it. We use that to know that the thing arriving is a Character. We then use Evennia's utils.inherits_from helper utility to get every NPC in the room can each of their newly created at_char_entered method.

Make sure to reload.

Let's create an NPC and make it aggressive. For the sake of this example, let's assume your name is "Anna" and that there is a room to the north of your current location.

> create/drop Orc:typeclasses.npcs.NPC
> north 
> south 
Orc says, Greetings, Anna!

Now let's turn the orc aggressive.

> set orc/is_aggressive = True 
> north 
> south 
Orc says, Graah! Die, Anna!

That's one easily aggravated Orc!