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 “mygame”.

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.

Edit mygame/typeclasses/characters.py and modify the Character class. The at_object_creation method also exists on the DefaultCharacter parent and will overload it. The get_abilities method is unique to our version of Character.

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.

Updating Yourself¶

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.

@update self

This will (only) re-run at_object_creation on yourself. You should henceforth be able to get the abilities successfully:

@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. from evennia shell):

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")

Using swap_typeclass to the same typeclass we already have will re-run the creation hooks (this is what the @update command does under the hood). From in-game you can do the same with @py:

@py typeclasses.myclass import MyClass;[obj.swap_typeclass(MyClass) for obj in
MyClass.objects.all()]

See the Object Typeclass tutorial for more help and the Typeclasses and Attributes page for detailed documentation about Typeclasses and Attributes.

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 Character but the error talks about DefaultObject. What has happened is that due to your unhandled SyntaxError 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 - DefaultObject

in order to keep your MUD running. Fix the original SyntaxError and reload the server. Evennia will then be able to use your modified Character class 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 SyntaxError happening at line 33 of 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¶

The @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 section.

Open 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:

    class CmdAbilities(BaseCommand):
        """
        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.py and add a new import to it near the top:
```
    from commands.command import CmdAbilities
```
In the CharacterCmdSet class, add the following near the bottom (it says where):
```
    self.add(CmdAbilities())
```
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

See the Adding a Command tutorial for more examples and the Commands section for detailed documentation about the Command system.

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.py for this example.
In the module import the base Object (typeclasses.objects.Object). This is empty by default, meaning it is just a proxy for the default evennia.DefaultObject.

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:

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).
Use @create/drop stone:wiseobject.WiseObject to create a talkative stone. If the @create command 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 @create command starts looking for Typeclasses in mygame/typeclasses/.
Use look stone to 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.

Note that 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 initialization.

The 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.