Objects

All in-game objects in Evennia, be it characters, chairs, monsters, rooms or hand grenades are represented by an Evennia Object. Objects form the core of Evennia and is probably what you’ll spend most time working with. Objects are Typeclassed entities.

How to create your own object types

An Evennia Object is, per definition, a Python class that includes evennia.DefaultObject among its parents. In mygame/typeclasses/objects.py there is already a class Object that inherits from DefaultObject and that you can inherit from. You can put your new typeclass directly in that module or you could organize your code in some other way. Here we assume we make a new module mygame/typeclasses/flowers.py:

# mygame/typeclasses/flowers.py

from typeclasses.objects import Object

class Rose(Object):
    """
    This creates a simple rose object
    """
    def at_object_creation(self):
        "this is called only once, when object is first created"
        # add a persistent attribute 'desc'
        # to object (silly example).
        self.db.desc = "This is a pretty rose with thorns."

You could save this in the mygame/typeclasses/objects.py (then you’d not need to import Object) or you can put it in a new module. Let’s say we do the latter, making a module typeclasses/flowers.py. Now you just need to point to the class Rose with the @create command to make a new rose:

@create/drop MyRose:flowers.Rose

What the @create command actually does is to use evennia.create_object. You can do the same thing yourself in code:

from evennia import create_object
new_rose = create_object("typeclasses.flowers.Rose", key="MyRose")

(The @create command will auto-append the most likely path to your typeclass, if you enter the call manually you have to give the full path to the class. The create.create_object function is powerful and should be used for all coded object creating (so this is what you use when defining your own building commands). Check out the ev.create_* functions for how to build other entities like Scripts).

This particular Rose class doesn’t really do much, all it does it make sure the attribute desc(which is what the look command looks for) is pre-set, which is pretty pointless since you will usually want to change this at build time (using the @desc command or using the Spawner). The Object typeclass offers many more hooks that is available to use though - see next section.

Properties and functions on Objects

Beyond the properties assigned to all typeclassed objects (see that page for a list of those), the Object also has the following custom properties:

  • aliases - a handler that allows you to add and remove aliases from this object. Use aliases.add() to add a new alias and aliases.remove() to remove one.
  • location - a reference to the object currently containing this object.
  • home is a backup location. The main motivation is to have a safe place to move the object to if its location is destroyed. All objects should usually have a home location for safety.
  • destination - this holds a reference to another object this object links to in some way. Its main use is for Exits, it’s otherwise usually unset.
  • nicks - as opposed to aliases, a Nick holds a convenient nickname replacement for a real name, word or sequence, only valid for this object. This mainly makes sense if the Object is used as a game character - it can then store briefer shorts, example so as to quickly reference game commands or other characters.or nicks.add(alias, realname) to add a new one.
  • player - this holds a reference to a connected Player controlling this object (if any). Note that this is set also if the controlling player is not currently online - to test if a player is online, use the has_player property instead.
  • sessions - if player field is set and the player is online, this is a list of all active sessions (server connections) to contact them through (it may be more than one if multiple connections are allowed in settings).
  • has_player - a shorthand for checking if an online player is currently connected to this object.
  • contents - this returns a list referencing all objects ‘inside’ this object (i,e. which has this object set as their location).
  • exits - this returns all objects inside this object that are Exits, that is, has the destination property set.

The last two properties are special:

  • cmdset - this is a handler that stores all command sets defined on the object (if any).
  • scripts - this is a handler that manages Scripts attached to the object (if any).

The Object also has a host of useful utility functions. See the function headers in src/objects/objects.py for their arguments and more details.

  • msg() - this function is used to send messages from the server to a player connected to this object.
  • msg_contents() - calls msg on all objects inside this object.
  • search() - this is a convenient shorthand to search for a specific object, at a given location or globally. It’s mainly useful when defining commands (in which case the object executing the command is named caller and one can do caller.search() to find objects in the room to operate on).
  • execute_cmd() - Lets the object execute the given string as if it was given on the command line.
  • move_to - perform a full move of this object to a new location. This is the main move method and will call all relevant hooks, do all checks etc.
  • clear_exits() - will delete all Exits to and from this object.
  • clear_contents() - this will not delete anything, but rather move all contents (except Exits) to their designated Home locations.
  • delete() - deletes this object, first calling clear_exits() and clear_contents().

The Object Typeclass defines many more hook methods beyond at_object_creation. Evennia calls these hooks at various points. When implementing your custom objects, you will inherit from the base parent and overload these hooks with your own custom code. See evennia.objects.objects for an updated list of all the available hooks or the API for DefaultObject here.

Subclasses of Object

There are three special subclasses of Object in default Evennia - Characters, Rooms and Exits. The reason they are separated is because these particular object types are fundamental, something you will always need and in some cases requires some extra attention in order to be recognized by the game engine (there is nothing stopping you from redefining them though). In practice they are all pretty similar to the base Object.

Characters

Characters are objects controlled by Players. When a new Player logs in to Evennia for the first time, a new Character object is created and the Player object is assigned to the player attribute. A Character object must have a Default Commandset set on itself at creation, or the player will not be able to issue any commands! If you just inherit your own class from evennia.DefaultCharacter and make sure to use super() to call the parent methods you should be fine. In mygame/typeclasses/characters.py is an empty Character class ready for you to modify.

Rooms

Rooms are the root containers of all other objects. The only thing really separating a room from any other object is that they have no location of their own and that default commands like @dig creates objects of this class - so if you want to expand your rooms with more functionality, just inherit from ev.DefaultRoom. In mygame/typeclasses/rooms.py is an empty Room class ready for you to modify.

Exits

Exits are objects connecting other objects (usually Rooms) together. An object named North or in might be an exit, as well as door, portal or jump out the window. An exit has two things that separate them from other objects. Firstly, their destination property is set and points to a valid object. This fact makes it easy and fast to locate exits in the database. Secondly, exits define a special Transit Command on themselves when they are created. This command is named the same as the exit object and will, when called, handle the practicalities of moving the character to the Exits’s destination - this allows you to just enter the name of the exit on its own to move around, just as you would expect.

The exit functionality is all defined on the Exit typeclass, so you could in principle completely change how exits work in your game (it’s not recommended though, unless you really know what you are doing). Exits are locked using an access_type called traverse and also make use of a few hook methods for giving feedback if the traversal fails. See evennia.DefaultExit for more info. In mygame/typeclasses/exits.py there is an empty Exit class for you to modify.

The process of traversing an exit is as follows:

  1. The traversing obj sends a command that matches the Exit-command name on the Exit object. The cmdhandler detects this and triggers the command defined on the Exit. Traversal always involves the “source” (the current location) and the destination (this is stored on the Exit object).
  2. The Exit command checks the traverse lock on the Exit object
  3. The Exit command triggers at_traverse(obj, destination) on the Exit object.
  4. In at_traverse, object.move_to(destination) is triggered. This triggers the following hooks, in order:
    1. obj.at_before_move(destination) - if this returns False, move is aborted.
    2. origin.at_before_leave(obj, destination)
    3. obj.announce_move_from(destination)
    4. Move is performed by changing obj.location from source location to destination.
    5. obj.announce_move_to(source)
    6. destination.at_object_receive(obj, source)
    7. obj.at_after_move(source)
  5. On the Exit object, at_after_traverse(obj, source) is triggered.
If the move fails for whatever reason, the Exit will look for an Attribute err_traverse on itself and display this as an error message. If this is not found, the Exit will instead call
at_failed_traverse(obj) on itself.