Traits¶

Contribution by Griatch 2020, based on code by Whitenoise and Ainneve contribs, 2014

A Trait represents a modifiable property on (usually) a Character. They can be used to represent everything from attributes (str, agi etc) to skills (hunting 10, swords 14 etc) and dynamically changing things like HP, XP etc. Traits differ from normal Attributes in that they track their changes and limit themselves to particular value-ranges. One can add/subtract from them easily and they can even change dynamically at a particular rate (like you being poisoned or healed).

Traits use Evennia Attributes under the hood, making them persistent (they survive a server reload/reboot).

Installation¶

Traits are always added to a typeclass, such as the Character class.

There are two ways to set up Traits on a typeclass. The first sets up the TraitHandler as a property .traits on your class and you then access traits as e.g. .traits.strength. The other alternative uses a TraitProperty, which makes the trait available directly as e.g. .strength. This solution also uses the TraitHandler, but you don’t need to define it explicitly. You can combine both styles if you like.

Traits with TraitHandler¶

Here’s an example for adding the TraitHandler to the Character class:

# mygame/typeclasses/objects.py

from evennia import DefaultCharacter
from evennia.utils import lazy_property
from evennia.contrib.rpg.traits import TraitHandler

# ...

class Character(DefaultCharacter):
    ...
    @lazy_property
    def traits(self):
        # this adds the handler as .traits
        return TraitHandler(self)


    def at_object_creation(self):
        # (or wherever you want)
        self.traits.add("str", "Strength", trait_type="static", base=10, mod=2)
        self.traits.add("hp", "Health", trait_type="gauge", min=0, max=100)
        self.traits.add("hunting", "Hunting Skill", trait_type="counter",
                        base=10, mod=1, min=0, max=100)

When adding the trait, you supply the name of the property (hunting) along with a more human-friendly name (“Hunting Skill”). The latter will show if you print the trait etc. The trait_type is important, this specifies which type of trait this is (see below).

TraitProperties¶

Using TraitProperties makes the trait available directly on the class, much like Django model fields. The drawback is that you must make sure that the name of your Traits don’t collide with any other properties/methods on your class.

# mygame/typeclasses/objects.py

from evennia import DefaultObject
from evennia.utils import lazy_property
from evennia.contrib.rpg.traits import TraitProperty

# ...

class Object(DefaultObject):
    ...
    strength = TraitProperty("Strength", trait_type="static", base=10, mod=2)
    health = TraitProperty("Health", trait_type="gauge", min=0, base=100, mod=2)
    hunting = TraitProperty("Hunting Skill", trait_type="counter", base=10, mod=1, min=0, max=100)

Note that the property-name will become the name of the trait and you don’t supply trait_key separately.

The .traits TraitHandler will still be created (it’s used under the hood. But it will only be created when the TraitProperty has been accessed at least once, so be careful if mixing the two styles. If you want to make sure .traits is always available, add the TraitHandler manually like shown earlier - the TraitProperty will by default use the same handler (.traits).

Using traits¶

A trait are entities added to the traithandler (if you use TraitProperty the handler is just created under the hood) after which one can access it as a property on the handler (similarly to how you can do .db.attrname for Attributes in Evennia).

All traits have a read-only field .value. This is only used to read out results, you never manipulate it directly (if you try, it will just remain unchanged). The .value is calculated based on combining fields, like .base and .mod - which fields are available and how they relate to each other depends on the trait type.

> obj.traits.strength.value
12                                  # base + mod

> obj.traits.strength.base += 5
obj.traits.strength.value
17

> obj.traits.hp.value
102                                 # base + mod

> obj.traits.hp.base -= 200
> obj.traits.hp.value
0                                   # min of 0

> obj.traits.hp.reset()
> obj.traits.hp.value
100

# you can also access properties like a dict
> obj.traits.hp["value"]
100

# you can store arbitrary data persistently for easy reference
> obj.traits.hp.effect = "poisoned!"
> obj.traits.hp.effect
"poisoned!"

# with TraitProperties:

> obj.hunting.value
12

> obj.strength.value += 5
> obj.strength.value
17

Relating traits to one another¶

From a trait you can access its own Traithandler as .traithandler. You can also find another trait on the same handler by using the Trait.get_trait("traitname") method.

> obj.strength.get_trait("hp").value
100

This is not too useful for the default trait types - they are all operating independently from one another. But if you create your own trait classes, you can use this to make traits that depend on each other.

For example, you could picture making a Trait that is the sum of the values of two other traits and capped by the value of a third trait. Such complex interactions are common in RPG rule systems but are by definition game specific.

See an example in the section about making your own Trait classes.

Trait types¶

All default traits have a read-only .value property that shows the relevant or ‘current’ value of the trait. Exactly what this means depends on the type of trait.

Traits can also be combined to do arithmetic with their .value, if both have a compatible type.

> trait1 + trait2
54

> trait1.value
3

> trait1 + 2
> trait1.value
5

Two numerical traits can also be compared (bigger-than etc), which is useful in all sorts of rule-resolution.

if trait1 > trait2:
    # do stuff

Trait¶

A single value of any type.

This is the ‘base’ Trait, meant to inherit from if you want to invent trait-types from scratch (most of the time you’ll probably inherit from some of the more advanced trait-type classes though).

Unlike other Trait-types, the single .value property of the base Trait can be editied. The value can hold any data that can be stored in an Attribute. If it’s an integer/float you can do arithmetic with it, but otherwise this acts just like a glorified Attribute.

> obj.traits.add("mytrait", "My Trait", trait_type="trait", value=30)
> obj.traits.mytrait.value
30

> obj.traits.mytrait.value = "stringvalue"
> obj.traits.mytrait.value
"stringvalue"

Static trait¶

value = base + mod

The static trait has a base value and an optional mod-ifier. A typical use of a static trait would be a Strength stat or Skill value. That is, something that varies slowly or not at all, and which may be modified in-place.

> obj.traits.add("str", "Strength", trait_type="static", base=10, mod=2)
> obj.traits.mytrait.value

12   # base + mod
> obj.traits.mytrait.base += 2
> obj.traits.mytrait.mod += 1
> obj.traits.mytrait.value
15

> obj.traits.mytrait.mod = 0
> obj.traits.mytrait.value
12

Counter¶

min/unset     base    base+mod                       max/unset
|--------------|--------|---------X--------X------------|
                              current    value
                                         = current
                                         + mod

A counter describes a value that can move from a base. The .current property is the thing usually modified. It starts at the .base. One can also add a modifier, which will both be added to the base and to current (forming .value). The min/max of the range are optional, a boundary set to None will remove it. A suggested use for a Counter Trait would be to track skill values.

> obj.traits.add("hunting", "Hunting Skill", trait_type="counter",
                   base=10, mod=1, min=0, max=100)
> obj.traits.hunting.value
11  # current starts at base + mod

> obj.traits.hunting.current += 10
> obj.traits.hunting.value
21

# reset back to base+mod by deleting current
> del obj.traits.hunting.current
> obj.traits.hunting.value
11
> obj.traits.hunting.max = None  # removing upper bound

# for TraitProperties, pass the args/kwargs of traits.add() to the
# TraitProperty constructor instead.

Counters have some extra properties:

.descs¶

The descs property is a dict {upper_bound:text_description}. This allows for easily storing a more human-friendly description of the current value in the interval. Here is an example for skill values between 0 and 10:

{0: "unskilled", 1: "neophyte", 5: "trained", 7: "expert", 9: "master"}

The keys must be supplied from smallest to largest. Any values below the lowest and above the highest description will be considered to be included in the closest description slot. By calling .desc() on the Counter, you will get the text matching the current value.

# (could also have passed descs= to traits.add())
> obj.traits.hunting.descs = {
    0: "unskilled", 10: "neophyte", 50: "trained", 70: "expert", 90: "master"}
> obj.traits.hunting.value
11

> obj.traits.hunting.desc()
"neophyte"
> obj.traits.hunting.current += 60
> obj.traits.hunting.value
71

> obj.traits.hunting.desc()
"expert"

.rate¶

The rate property defaults to 0. If set to a value different from 0, it allows the trait to change value dynamically. This could be used for example for an attribute that was temporarily lowered but will gradually (or abruptly) recover after a certain time. The rate is given as change of the current .value per-second, and this will still be restrained by min/max boundaries, if those are set.

It is also possible to set a .ratetarget, for the auto-change to stop at (rather than at the min/max boundaries). This allows the value to return to a previous value.

> obj.traits.hunting.value
71

> obj.traits.hunting.ratetarget = 71
# debuff hunting for some reason
> obj.traits.hunting.current -= 30
> obj.traits.hunting.value
41

> obj.traits.hunting.rate = 1  # 1/s increase
# Waiting 5s
> obj.traits.hunting.value
46

# Waiting 8s
> obj.traits.hunting.value
54

# Waiting 100s
> obj.traits.hunting.value
71    # we have stopped at the ratetarget

> obj.traits.hunting.rate = 0  # disable auto-change

Note that when retrieving the current, the result will always be of the same type as the .base even rate is a non-integer value. So if base is an int (default), the current value will also be rounded the closest full integer. If you want to see the exact current value, set base to a float - you will then need to use round() yourself on the result if you want integers.

.percent()¶

If both min and max are defined, the .percent() method of the trait will return the value as a percentage.

> obj.traits.hunting.percent()
"71.0%"

> obj.traits.hunting.percent(formatting=None)
71.0

Gauge¶

This emulates a [fuel-] gauge that empties from a base+mod value.

min/0                                            max=base+mod
 |-----------------------X---------------------------|
                       value
                      = current

The .current value will start from a full gauge. The .max property is read-only and is set by .base + .mod. So contrary to a Counter, the .mod modifier only applies to the max value of the gauge and not the current value. The minimum bound defaults to 0 if not set explicitly.

This trait is useful for showing commonly depletable resources like health, stamina and the like.

> obj.traits.add("hp", "Health", trait_type="gauge", base=100)
> obj.traits.hp.value  # (or .current)
100

> obj.traits.hp.mod = 10
> obj.traits.hp.value
110

> obj.traits.hp.current -= 30
> obj.traits.hp.value
80

The Gauge trait is subclass of the Counter, so you have access to the same methods and properties where they make sense. So gauges can also have a .descs dict to describe the intervals in text, and can use .percent() to get how filled it is as a percentage etc.

The .rate is particularly relevant for gauges - useful for everything from poison slowly draining your health, to resting gradually increasing it.

Expanding with your own Traits¶

A Trait is a class inhering from evennia.contrib.rpg.traits.Trait (or from one of the existing Trait classes).

# in a file, say, 'mygame/world/traits.py'

from evennia.contrib.rpg.traits import StaticTrait

class RageTrait(StaticTrait):

    trait_type = "rage"
    default_keys = {
        "rage": 0
    }

    def berserk(self):
        self.mod = 100

    def sedate(self):
        self.mod = 0

Above is an example custom-trait-class “rage” that stores a property “rage” on itself, with a default value of 0. This has all the functionality of a Trait - for example, if you do del on the rage property, it will be set back to its default (0). Above we also added some helper methods.

To add your custom RageTrait to Evennia, add the following to your settings file (assuming your class is in mygame/world/traits.py):

TRAIT_CLASS_PATHS = ["world.traits.RageTrait"]

Reload the server and you should now be able to use your trait:

> obj.traits.add("mood", "A dark mood", rage=30, trait_type='rage')
> obj.traits.mood.rage
30

Remember that you can use .get_trait("name") to access other traits on the same handler. Let’s say that the rage modifier is actually limited by the characters’s current STR value times 3, with a max of 100:

class RageTrait(StaticTrait):
    #...
    def berserk(self):
        self.mod = min(100, self.get_trait("STR").value * 3)

as TraitProperty¶

class Character(DefaultCharacter):
    rage = TraitProperty("A dark mood", rage=30, trait_type='rage')

Adding additional TraitHandlers¶

Sometimes, it is easier to top-level classify traits, such as stats, skills, or other categories of traits you want to handle independantly of each other. Here is an example showing an example on the object typeclass, expanding on the first installation example:

# mygame/typeclasses/objects.py

from evennia import DefaultCharacter
from evennia.utils import lazy_property
from evennia.contrib.rpg.traits import TraitHandler

# ...

class Character(DefaultCharacter):
    ...
    @lazy_property
    def traits(self):
        # this adds the handler as .traits
        return TraitHandler(self)

    @lazy_property
    def stats(self):
        # this adds the handler as .stats
        return TraitHandler(self, db_attribute_key="stats")

    @lazy_property
    def skills(self):
        # this adds the handler as .skills
        return TraitHandler(self, db_attribute_key="skills")


    def at_object_creation(self):
        # (or wherever you want)
        self.stats.add("str", "Strength", trait_type="static", base=10, mod=2)
        self.traits.add("hp", "Health", trait_type="gauge", min=0, max=100)
        self.skills.add("hunting", "Hunting Skill", trait_type="counter",
                        base=10, mod=1, min=0, max=100)

Rememebr that the .get_traits() method only works for accessing Traits within the same TraitHandler.

This document page is generated from evennia/contrib/rpg/traits/README.md. Changes to this file will be overwritten, so edit that file rather than this one.

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