-`inventory_use_slot` - some items can be worn or wielded. For example, a helmet needs to be worn on the head and a shield in the shield hand. Some items can't be used this way at all, but only belong in the backpack.
The problem with this is that if we want to make a new object of `size 3` and `value 20`, we have to make a new class for it. We can't change it on the fly because the change would only be in memory and be lost on next server reload.
Because we use `AttributeProperties`, we can set `size` and `value` to whatever we like when we create the object (or later), and the Attributes will remember our changes to that object indefinitely.
To make this a little more efficient, we use `autocreate=False`. Normally when you create a new object with defined `AttributeProperties`, a matching `Attribute` is immediately created at the same time. So normally, the object would be created along with two Attributes `size` and `value`. With `autocreate=False`, no Attribute will be created _unless the default is changed_. That is, as long as your object has `size=1` no database `Attribute` will be created at all. This saves time and resources when creating large number of objects.
The drawback is that since no Attribute is created you can't refer to it with `obj.db.size` or `obj.attributes.get("size")`_unless you change its default_. You also can't query the database for all objects with `size=1`, since most objects would not yet have an in-database
We do a tricky thing here, converting our `.obj_type` to one or more [Tags](../../../Components/Tags.md). Tagging the object like this means you can later efficiently find all objects of a given type (or combination of
We allow `.obj_type` to be given as a single value or a list of values. We use `make_iter` from the evennia utility library to make sure we don't balk at either. This means you could have a Shield that is also Magical, for example.
In `at_pre_use` we check if we have specified a target (heal someone else or throw a fire bomb at an enemy?), making sure we are in the same location. We also make sure we have `usages` left. In `at_post_use` we make sure to tick off usages.
What exactly each consumable does will vary - we will need to implement children of this class later, overriding `at_use` with different effects.
All weapons need properties that describe how efficient they are in battle. To 'use' a weapon means to attack with it, so we can let the weapon itself handle all logic around performing an attack. Having the attack code on the weapon also means that if we in the future wanted a weapon doing something special on-attack (for example, a vampiric sword that heals the attacker when hurting the enemy), we could easily add that on the weapon subclass in question without modifying other code.
In EvAdventure, we will assume all weapons (including bows etc) are used in the same location as the target. Weapons also have a `quality` attribute that gets worn down if the user rolls a critical failure. Once quality is down to 0, the weapon is broken and needs to be repaired.
The `quality` is something we need to track in _Knave_. When getting critical failures on attacks, a weapon's quality will go down. When it reaches 0, it will break.
In the `use` method we make use of the `rules` module we [created earlier](Beginner-Tutorial-Rules) to perform all the dice rolls needed to resolve the attack.
This code requires some additional explanation:
```python
location.msg_contents(
f"$You() $conj(attack) $you({target.key}) with {self.key}: {txt}",
from_obj=attacker,
mapping={target.key: target},
)
```
`location.msg_contents` sends a message to everyone in `location`. Since people will usually notice if you swing a sword at somone, this makes sense to tell people about. This message should however look _different_ depending on who sees it.
I should see:
You attack Grendel with sword: <dicerollresults>
Others should see
Beowulf attacks Grendel with sword: <dicerollresults>
And Grendel should see
Beowulf attacks you with sword: <dicerollresults>
We provide the following string to `msg_contents`:
```python
f"$You() $conj(attack) $You({target.key}) with {self.key}: {txt}"
```
The `{...}` are normal f-string formatting markers like those we have used before. The `$func(...)` bits are [Evennnia FuncParser](FuncParser) function calls. FuncParser calls are executed as functions and the result replaces their position in the string. As this string is parsed by Evennia, this is what happens:
First the f-string markers are replaced, so that we get this:
```python
"$You() $cobj(attack) $you(Grendel) with sword: \n rolled 8 on d20 ..."
```
Next the funcparser functions are run:
-`$You()` becomes the name or `You` depending on if the string is to be sent to that object or not. It uses the `from_obj=` kwarg to the `msg_contents` method to know this. Since `msg_contents=attacker` , this becomes `You` or `Beowulf` in this example.
-`$you(Grendel)` looks for the `mapping=` kwarg to `msg_contents` to determine who should be addressed here. If will replace this with the display name or the lowercase `you`. We have added `mapping={target.key: target}` - that is `{"Grendel": <grendel_obj>}`. So this will become `you` or `Grendel` depending on who sees the string.
-`$conj(attack)`_conjugates_ the verb depending on who sees it. The result will be `You attack ...` or `Beowulf attacks` (note the extra `s`).
A few funcparser calls compacts all these points of view into one string!
In _Knave_, anyone can use magic if they are wielding a rune stone (our name for spell books) in both hands. You can only use a rune stone once per rest. So a rune stone is an example of a 'magical weapon' that is also a 'consumable' of sorts.
We make the rune stone a mix of weapon and consumable. Note that we don't have to add `.uses` again, it's inherited from `EvAdventureConsumable` parent. The `at_pre_use` and `use` methods are also inherited; we only override `at_post_use` since we don't want the runestone to be deleted when it runs out of uses.
Exactly what rune stones _do_ will be implemented in the `at_use` methods of subclasses to this base class. Since magic in _Knave_ tends to be pretty custom, it makes sense that it will lead to a lot of custom code.
Armor, shields and helmets increase the `ARMOR` stat of the character. In _Knave_, what is stored is the defense value of the armor (values 11-20). We will instead store the 'armor bonus' (1-10). As we know, defending is always `bonus + 10`, so the result will be the same - this means we can use `Ability.ARMOR` as any other defensive ability without worrying about a special case.
When we don't have any weapons, we'll be using our bare fists to fight.
We will use this in the upcoming [Equipment tutorial lesson](./Beginner-Tutorial-Equipment.md) to represent when you have 'nothing' in your hands. This way we don't need to add any special case for this.
Since everyone's empty hands are the same (in our game), we create _one_`Bare hands` weapon object that everyone shares. We do this by searching for the object with `search_object` (the `.first()` means we grab the first one even if we should by accident have created multiple hands, see [The Django querying tutorial](Beginner-Tutorial-Django-queries) for more info). If we find none, we create it. This way the `BARE_HANDS` object can be used by everyone (we just need to import `objects.BARE_HANDS`).
Remember the `get_obj_stats` function from the [Utility Tutorial](./Beginner-Tutorial-Utilities.md) earlier? We had to use dummy-values since we didn't yet know how we would store properties on Objects in the game.
When you change this function you must also update the related unit test - so your existing test becomes a nice way to test your new Objects as well! Add more tests showing the output of feeding different object-types to `get_obj_stats`.
