First Steps Coding¶
This section gives a brief step-by-step introduction on how to set up Evennia for the first time so you can modify and overload the defaults easily. You should only need to do these steps once. It also walks through you making your first few tweaks.
Before continuing, make sure you have Evennia installed and running by following the Getting
Started instructions. You should have initialized a new game folder with the
evennia --init foldername command. We will in the following assume this folder is called
It might be a good idea to eye through the brief Coding Introduction too
(especially the recommendations in the section about the evennia “flat” API and about using
evennia shell will help you here and in the future).
To follow this tutorial you also need to know the basics of operating your computer’s terminal/command line. You also need to have a text editor to edit and create source text files. There are plenty of online tutorials on how to use the terminal and plenty of good free text editors. We will assume these things are already familiar to you henceforth.
Your First Changes¶
Below are some first things to try with your new custom modules. You can test these to get a feel for the system. See also Tutorials for more step-by-step help and special cases.
Tweak Default Character¶
We will add some simple rpg attributes to our default Character. In the next section we will follow up with a new command to view those attributes.
mygame/typeclasses/characters.pyand modify the
at_object_creationmethod also exists on the
DefaultCharacterparent and will overload it. The
get_abilitiesmethod is unique to our version of
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class Character(DefaultCharacter): # [...] def at_object_creation(self): """ Called only at initial creation. This is a rather silly example since ability scores should vary from Character to Character and is usually set during some character generation step instead. """ #set persistent attributes self.db.strength = 5 self.db.agility = 4 self.db.magic = 2 def get_abilities(self): """ Simple access method to return ability scores as a tuple (str,agi,mag) """ return self.db.strength, self.db.agility, self.db.magic
Reload the server (you will still be connected to the game after doing this). Note that if you examine yourself you will not see any new Attributes appear yet. Read the next section to understand why.
It’s important to note that the new Attributes we added above will only be stored on
newly created characters. The reason for this is simple: The
at_object_creation method, where we
added those Attributes, is per definition only called when the object is first created, then never
again. This is usually a good thing since those Attributes may change over time - calling that hook
would reset them back to start values. But it also means that your existing character doesn’t have
them yet. You can see this by calling the
get_abilities hook on yourself at this point:
# (you have to be superuser to use @py) @py self.get_abilities() <<< (None, None, None)
This is easily remedied.
This will (only) re-run
at_object_creation on yourself. You should henceforth be able to get the
@py self.get_abilities() <<< (5, 4, 2)
This is something to keep in mind if you start building your world before your code is stable -
startup-hooks will not (and should not) automatically run on existing objects - you have to update
your existing objects manually. Luckily this is a one-time thing and pretty simple to do. If the
typeclass you want to update is in
typeclasses.myclass.MyClass, you can do the following (e.g.
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from typeclasses.myclass import MyClass # loop over all MyClass instances in the database # and call .swap_typeclass on them for obj in MyClass.objects.all(): obj.swap_typeclass(MyClass, run_start_hooks="at_object_creation")
swap_typeclass to the same typeclass we already have will re-run the creation hooks (this is
@update command does under the hood). From in-game you can do the same with
@py typeclasses.myclass import MyClass;[obj.swap_typeclass(MyClass) for obj in MyClass.objects.all()]
Troubleshooting: Updating Yourself¶
One may experience errors for a number of reasons. Common beginner errors are spelling mistakes,
wrong indentations or code omissions leading to a
SyntaxError. Let’s say you leave out a colon
from the end of a class function like so:
def at_object_creation(self). The client will reload
without issue. However, if you look at the terminal/console (i.e. not in-game), you will see
Evennia complaining (this is called a traceback):
Traceback (most recent call last): File "C:\mygame\typeclasses\characters.py", line 33 def at_object_creation(self) ^ SyntaxError: invalid syntax
Evennia will still be restarting and following the tutorial, doing
@py self.get_abilities() will
return the right response
(None, None, None). But when attempting to
@typeclass/force self you
will get this response:
AttributeError: 'DefaultObject' object has no attribute 'get_abilities'
The full error will show in the terminal/console but this is confusing since you did add
get_abilities before. Note however what the error says - you (
self) should be a
the error talks about
DefaultObject. What has happened is that due to your unhandled
earlier, Evennia could not load the
character.py module at all (it’s not valid Python). Rather
than crashing, Evennia handles this by temporarily falling back to a safe default -
in order to keep your MUD running. Fix the original
SyntaxErrorand reload the server. Evennia will then be able to use your modified
Characterclass again and things should work.
Note: Learning how to interpret an error traceback is a critical skill for anyone learning Python. Full tracebacks will appear in the terminal/Console you started Evennia from. The traceback text can sometimes be quite long, but you are usually just looking for the last few lines: The description of the error and the filename + line number for where the error occurred. In the example above, we see it’s a
mygame\typeclasses\characters.py. In this case it even points out where on the line it encountered the error (the missing colon). Learn to read tracebacks and you’ll be able to resolve the vast majority of common errors easily.
Add a New Default Command¶
@py command used above is only available to privileged users. We want any player to be able to
see their stats. Let’s add a new command to list the abilities we added in the previous
mygame/commands/command.py. You could in principle put your command anywhere but this module has all the imports already set up along with some useful documentation. Make a new class at the bottom of this file:
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class CmdAbilities(Command): """ List abilities Usage: abilities Displays a list of your current ability values. """ key = "abilities" aliases = ["abi"] lock = "cmd:all()" help_category = "General" def func(self): "implements the actual functionality" str, agi, mag = self.caller.get_abilities() string = "STR: %s, AGI: %s, MAG: %s" % (str, agi, mag) self.caller.msg(string)
Next you edit
mygame/commands/default_cmdsets.pyand add a new import to it near the top:
from commands.command import CmdAbilities
CharacterCmdSetclass, add the following near the bottom (it says where):
Reload the server (noone will be disconnected by doing this).
You (and anyone else) should now be able to use
abilities (or its alias
abi) as part of your
normal commands in-game:
abilities STR: 5, AGI: 4, MAG: 2
Make a New Type of Object¶
Let’s test to make a new type of object. This example is an “wise stone” object that returns some random comment when you look at it, like this:
> look stone A very wise stone This is a very wise old stone. It grumbles and says: 'The world is like a rock of chocolate.'
Create a new module in
mygame/typeclasses/. Name it
wiseobject.pyfor this example.
In the module import the base
typeclasses.objects.Object). This is empty by default, meaning it is just a proxy for the default
Make a new class in your module inheriting from
Object. Overload hooks on it to add new functionality. Here is an example of how the file could look:
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from random import choice from typeclasses.objects import Object class WiseObject(Object): """ An object speaking when someone looks at it. We assume it looks like a stone in this example. """ def at_object_creation(self): "Called when object is first created" self.db.wise_texts = \ ["Stones have feelings too.", "To live like a stone is to not have lived at all.", "The world is like a rock of chocolate."] def return_appearance(self, looker): """ Called by the look command. We want to return a wisdom when we get looked at. """ # first get the base string from the # parent's return_appearance. string = super().return_appearance(looker) wisewords = "\n\nIt grumbles and says: '%s'" wisewords = wisewords % choice(self.db.wise_texts) return string + wisewords
Check your code for bugs. Tracebacks will appear on your command line or log. If you have a grave Syntax Error in your code, the source file itself will fail to load which can cause issues with the entire cmdset. If so, fix your bug and reload the server from the command line (noone will be disconnected by doing this).
@create/drop stone:wiseobject.WiseObjectto create a talkative stone. If the
@createcommand spits out a warning or cannot find the typeclass (it will tell you which paths it searched), re-check your code for bugs and that you gave the correct path. The
@createcommand starts looking for Typeclasses in
look stoneto test. You will see the default description (”You see nothing special”) followed by a random message of stony wisdom. Use
@desc stone = This is a wise old stone.to make it look nicer. See the Builder Docs for more information.
at_object_creation is only called once, when the stone is first created. If you make
changes to this method later, already existing stones will not see those changes. As with the
Character example above you can use
@typeclass/force to tell the stone to re-run its
at_object_creation is a special case though. Changing most other aspects of the typeclass does
not require manual updating like this - you just need to
@reload to have all changes applied
automatically to all existing objects.
Where to Go From Here?¶
There are more Tutorials, including one for building a whole little MUSH-like game - that is instructive also if you have no interest in MUSHes per se. A good idea is to also get onto the IRC chat and the mailing list to get in touch with the community and other developers.