# Handling Equipment
In _Knave_, you have a certain number of inventory "slots". The amount of slots is given by `CON + 10`.
All items (except coins) have a `size`, indicating how many slots it uses. You can't carry more items
than you have slot-space for. Also items wielded or worn count towards the slots.
We still need to track what the character is using however: What weapon they have readied affects the damage
they can do. The shield, helmet and armor they use affects their defense.
We have already set up the possible 'wear/wield locations' when we defined our Objects
[in the previous lesson](./Beginner-Tutorial-Objects.md). This is what we have in `enums.py`:
```python
# mygame/evadventure/enums.py
# ...
class WieldLocation(Enum):
BACKPACK = "backpack"
WEAPON_HAND = "weapon_hand"
SHIELD_HAND = "shield_hand"
TWO_HANDS = "two_handed_weapons"
BODY = "body" # armor
HEAD = "head" # helmets
```
Basically, all the weapon/armor locations are exclusive - you can only have one item in each (or none).
The BACKPACK is special - it contains any number of items (up to the maximum slot usage).
## EquipmentHandler that saves
> Create a new module `mygame/evadventure/equipment.py`.
```{sidebar}
If you want to understand more about behind how Evennia uses handlers, there is a
[dedicated tutorial](../../Tutorial-Persistent-Handler.md) talking about the principle.
```
In default Evennia, everything you pick up will end up "inside" your character object (that is, have
you as its `.location`). This is called your _inventory_ and has no limit. We will keep 'moving items into us'
when we pick them up, but we will add more functionality using an _Equipment handler_.
A handler is (for our purposes) an object that sits "on" another entity, containing functionality
for doing one specific thing (managing equipment, in our case).
This is the start of our handler:
```python
# in mygame/evadventure/equipment.py
from .enums import WieldLocation
class EquipmentHandler:
save_attribute = "inventory_slots"
def __init__(self, obj):
# here obj is the character we store the handler on
self.obj = obj
self._load()
def _load(self):
"""Load our data from an Attribute on `self.obj`"""
self.slots = self.obj.attributes.get(
self.save_attribute,
category="inventory",
default={
WieldLocation.WEAPON_HAND: None,
WieldLocation.SHIELD_HAND: None,
WieldLocation.TWO_HANDS: None,
WieldLocation.BODY: None,
WieldLocation.HEAD: None,
WieldLocation.BACKPACK: []
}
)
def _save(self):
"""Save our data back to the same Attribute"""
self.obj.attributes.add(self.save_attribute, self.slots, category="inventory")
```
This is a compact and functional little handler. Before analyzing how it works, this is how
we will add it to the Character:
```python
# mygame/evadventure/characters.py
# ...
from evennia.utils.utils import lazy_property
from .equipment import EquipmentHandler
# ...
class EvAdventureCharacter(LivingMixin, DefaultCharacter):
# ...
@lazy_property
def equipment(self):
return EquipmentHandler(self)
```
After reloading the server, the equipment-handler will now be accessible on character-instances as
character.equipment
The `@lazy_property` works such that it will not load the handler until someone actually tries to
fetch it with `character.equipment`. When that
happens, we start up the handler and feed it `self` (the `Character` instance itself). This is what
enters `__init__` as `.obj` in the `EquipmentHandler` code above.
So we now have a handler on the character, and the handler has a back-reference to the character it sits
on.
Since the handler itself is just a regular Python object, we need to use the `Character` to store
our data - our _Knave_ "slots". We must save them to the database, because we want the server to remember
them even after reloading.
Using `self.obj.attributes.add()` and `.get()` we save the data to the Character in a specially named
[Attribute](../../../Components/Attributes.md). Since we use a `category`, we are unlikely to collide with
other Attributes.
Our storage structure is a `dict` with keys after our available `WieldLocation` enums. Each can only
have one item except `WieldLocation.BACKPACK`, which is a list.
## Connecting the EquipmentHandler
Whenever an object leaves from one location to the next, Evennia will call a set of _hooks_ (methods) on the
object that moves, on the source-location and on its destination. This is the same for all moving things -
whether it's a character moving between rooms or an item being dropping from your hand to the ground.
We need to tie our new `EquipmentHandler` into this system. By reading the doc page on [Objects](../../../Components/Objects.md),
or looking at the [DefaultObject.move_to](evennia.objects.objects.DefaultObject.move_to) docstring, we'll
find out what hooks Evennia will call. Here `self` is the object being moved from
`source_location` to `destination`:
1. `self.at_pre_move(destination)` (abort if return False)
2. `source_location.at_pre_object_leave(self, destination)` (abort if return False)
3. `destination.at_pre_object_receive(self, source_location)` (abort if return False)
4. `source_location.at_object_leave(self, destination)`
5. `self.announce_move_from(destination)`
6. (move happens here)
7. `self.announce_move_to(source_location)`
8. `destination.at_object_receive(self, source_location)`
9. `self.at_post_move(source_location)`
All of these hooks can be overridden to customize movement behavior. In this case we are interested in
controlling how items 'enter' and 'leave' our character - being 'inside' the character is the same as
them 'carrying' it. We have three good hook-candidates to use for this.
- `.at_pre_object_receive` - used to check if you can actually pick something up, or if your equipment-store is full.
- `.at_object_receive` - used to add the item to the equipmenthandler
- `.at_object_leave` - used to remove the item from the equipmenthandler
You could also picture using `.at_pre_object_leave` to restrict dropping (cursed?) items, but
we will skip that for this tutorial.
```python
# mygame/evadventure/character.py
# ...
class EvAdventureCharacter(LivingMixin, DefaultCharacter):
# ...
def at_pre_object_receive(self, moved_object, source_location, **kwargs):
"""Called by Evennia before object arrives 'in' this character (that is,
if they pick up something). If it returns False, move is aborted.
"""
return self.equipment.validate_slot_usage(moved_object)
def at_object_receive(self, moved_object, source_location, **kwargs):
"""
Called by Evennia when an object arrives 'in' the character.
"""
self.equipment.add(moved_object)
def at_object_leave(self, moved_object, destination, **kwargs):
"""
Called by Evennia when object leaves the Character.
"""
self.equipment.remove(moved_object)
```
Above we have assumed the `EquipmentHandler` (`.equipment`) has methods `.validate_slot_usage`,
`.add` and `.remove`. But we haven't actually added them yet - we just put some reasonable names! Before
we can use this, we need to go actually adding those methods.
## Expanding the Equipmenthandler
## `.validate_slot_usage`
Let's start with implementing the first method we came up with above, `validate_slot_usage`:
```python
# mygame/evadventure/equipment.py
from .enums import WieldLocation, Ability
class EquipmentError(TypeError):
"""All types of equipment-errors"""
pass
class EquipmentHandler:
# ...
@property
def max_slots(self):
"""Max amount of slots, based on CON defense (CON + 10)"""
return getattr(self.obj, Ability.CON.value, 1) + 10
def count_slots(self):
"""Count current slot usage"""
slots = self.slots
wield_usage = sum(
getattr(slotobj, "size", 0) or 0
for slot, slotobj in slots.items()
if slot is not WieldLocation.BACKPACK
)
backpack_usage = sum(
getattr(slotobj, "size", 0) or 0 for slotobj in slots[WieldLocation.BACKPACK]
)
return wield_usage + backpack_usage
def validate_slot_usage(self, obj):
"""
Check if obj can fit in equipment, based on its size.
"""
if not inherits_from(obj, EvAdventureObject):
# in case we mix with non-evadventure objects
raise EquipmentError(f"{obj.key} is not something that can be equipped.")
size = obj.size
max_slots = self.max_slots
current_slot_usage = self.count_slots()
return current_slot_usage + size <= max_slots:
```
```{sidebar}
The `@property` decorator turns a method into a property so you don't need to 'call' it.
That is, you can access `.max_slots` instead of `.max_slots()`. In this case, it's just a
little less to type.
```
We add two helpers - the `max_slots` _property_ and `count_slots`, a method that calculate the current
slots being in use. Let's figure out how they work.
### `.max_slots`
For `max_slots`, remember that `.obj` on the handler is a back-reference to the `EvAdventureCharacter` we
put this handler on. `getattr` is a Python method for retrieving a named property on an object.
The `Enum` `Ability.CON.value` is the string `Constitution` (check out the
[first Utility and Enums tutorial](./Beginner-Tutorial-Utilities.md) if you don't recall).
So to be clear,
```python
getattr(self.obj, Ability.CON.value) + 10
```
is the same as writing
```python
getattr(your_character, "Constitution") + 10
```
which is the same as doing something like this:
```python
your_character.Constitution + 10
```
In our code we write `getattr(self.obj, Ability.CON.value, 1)` - that extra `1` means that if there
should happen to _not_ be a property "Constitution" on `self.obj`, we should not error out but just
return 1.
### `.count_slots`
In this helper we use two Python tools - the `sum()` function and a
[list comprehension](https://www.w3schools.com/python/python_lists_comprehension.asp). The former
simply adds the values of any iterable together. The latter is a more efficient way to create a list:
new_list = [item for item in some_iterable if condition]
all_above_5 = [num for num in range(10) if num > 5] # [6, 7, 8, 9]
all_below_5 = [num for num in range(10) if num < 5] # [0, 1, 2, 3, 4]
To make it easier to understand, try reading the last line above as "for every number in the range 0-9,
pick all with a value below 5 and make a list of them". You can also embed such comprehensions
directly in a function call like `sum()` without using `[]` around it.
In `count_slots` we have this code:
```python
wield_usage = sum(
getattr(slotobj, "size", 0)
for slot, slotobj in slots.items()
if slot is not WieldLocation.BACKPACK
)
```
We should be able to follow all except `slots.items()`. Since `slots` is a `dict`, we can use `.items()`
to get a sequence of `(key, value)` pairs. We store these in `slot` and `slotobj`. So the above can
be understood as "for every `slot` and `slotobj`-pair in `slots`, check which slot location it is.
If it is _not_ in the backpack, get its size and add it to the list. Sum over all these
sizes".
A less compact but maybe more readonable way to write this would be:
```python
backpack_item_sizes = []
for slot, slotobj in slots.items():
if slot is not WieldLocation.BACKPACK:
size = getattr(slotobj, "size", 0)
backpack_item_sizes.append(size)
wield_usage = sum(backpack_item_sizes)
```
The same is done for the items actually in the BACKPACK slot. The total sizes are added
together.
### Validating slots
With these helpers in place, `validate_slot_usage` now becomes simple. We use `max_slots` to see how much we can carry.
We then get how many slots we are already using (with `count_slots`) and see if our new `obj`'s size
would be too much for us.
## `.add` and `.remove`
We will make it so `.add` puts something in the `BACKPACK` location and `remove` drops it, wherever
it is (even if it was in your hands).
```python
# mygame/evadventure/equipment.py
from .enums import WieldLocation, Ability
# ...
class EquipmentHandler:
# ...
def add(self, obj):
"""
Put something in the backpack.
"""
self.validate_slot_usage(obj)
self.slots[WieldLocation.BACKPACK].append(obj)
self._save()
def remove(self, slot):
"""
Remove contents of a particular slot, for
example `equipment.remove(WieldLocation.SHIELD_HAND)`
"""
slots = self.slots
ret = []
if slot is WieldLocation.BACKPACK:
# empty entire backpack!
ret.extend(slots[slot])
slots[slot] = []
else:
ret.append(slots[slot])
slots[slot] = None
if ret:
self._save()
return ret
```
Both of these should be straight forward to follow. In `.add`, we make use of `validate_slot_usage` to
double-check we can actually fit the thing, then we add the item to the backpack.
In `.delete`, we allow emptying by `WieldLocation` - we figure out what slot it is and return
the item within (if any). If we gave `BACKPACK` as the slot, we empty the backpack and
return all items.
Whenever we change the equipment loadout we must make sure to `._save()` the result, or it will
be lost after a server reload.
## Moving things around
With the help of `.remove()` and `.add()` we can get things in and out of the `BACKPACK` equipment
location. We also need to grab stuff from the backpack and wield or wear it. We add a `.move` method
on the `EquipmentHandler` to do this:
```python
# mygame/evadventure/equipment.py
from .enums import WieldLocation, Ability
# ...
class EquipmentHandler:
# ...
def move(self, obj):
"""Move object from backpack to its intended `inventory_use_slot`."""
# make sure to remove from equipment/backpack first, to avoid double-adding
self.remove(obj)
slots = self.slots
use_slot = getattr(obj, "inventory_use_slot", WieldLocation.BACKPACK)
to_backpack = []
if use_slot is WieldLocation.TWO_HANDS:
# two-handed weapons can't co-exist with weapon/shield-hand used items
to_backpack = [slots[WieldLocation.WEAPON_HAND], slots[WieldLocation.SHIELD_HAND]]
slots[WieldLocation.WEAPON_HAND] = slots[WieldLocation.SHIELD_HAND] = None
slots[use_slot] = obj
elif use_slot in (WieldLocation.WEAPON_HAND, WieldLocation.SHIELD_HAND):
# can't keep a two-handed weapon if adding a one-handed weapon or shield
to_backpack = [slots[WieldLocation.TWO_HANDS]]
slots[WieldLocation.TWO_HANDS] = None
slots[use_slot] = obj
elif use_slot is WieldLocation.BACKPACK:
# it belongs in backpack, so goes back to it
to_backpack = [obj]
else:
# for others (body, head), just replace whatever's there
replaced = [obj]
slots[use_slot] = obj
for to_backpack_obj in to_backpack:
# put stuff in backpack
slots[use_slot].append(to_backpack_obj)
# store new state
self._save()
```
Here we remember that every `EvAdventureObject` has an `inventory_use_slot` property that tells us where
it goes. So we just need to move the object to that slot, replacing whatever is in that place
from before. Anything we replace goes back to the backpack.
## Get everything
In order to visualize our inventory, we need some method to get everything we are carrying.
```python
# mygame/evadventure/equipment.py
from .enums import WieldLocation, Ability
# ...
class EquipmentHandler:
# ...
def all(self):
"""
Get all objects in inventory, regardless of location.
"""
slots = self.slots
lst = [
(slots[WieldLocation.WEAPON_HAND], WieldLocation.WEAPON_HAND),
(slots[WieldLocation.SHIELD_HAND], WieldLocation.SHIELD_HAND),
(slots[WieldLocation.TWO_HANDS], WieldLocation.TWO_HANDS),
(slots[WieldLocation.BODY], WieldLocation.BODY),
(slots[WieldLocation.HEAD], WieldLocation.HEAD),
] + [(item, WieldLocation.BACKPACK) for item in slots[WieldLocation.BACKPACK]]
return lst
```
Here we get all the equipment locations and add their contents together into a list of tuples
`[(item, WieldLocation), ...]`. This is convenient for display.
## Weapon and armor
It's convenient to have the `EquipmentHandler` easily tell you what weapon is currently wielded
and what _armor_ level all worn equipment provides. Otherwise you'd need to figure out what item is
in which wield-slot and to add up armor slots manually every time you need to know.
```python
# mygame/evadventure/equipment.py
from .objects import WeaponEmptyHand
from .enums import WieldLocation, Ability
# ...
class EquipmentHandler:
# ...
@property
def armor(self):
slots = self.slots
return sum(
(
# armor is listed using its defense, so we remove 10 from it
# (11 is base no-armor value in Knave)
getattr(slots[WieldLocation.BODY], "armor", 1),
# shields and helmets are listed by their bonus to armor
getattr(slots[WieldLocation.SHIELD_HAND], "armor", 0),
getattr(slots[WieldLocation.HEAD], "armor", 0),
)
)
@property
def weapon(self):
# first checks two-handed wield, then one-handed; the two
# should never appear simultaneously anyhow (checked in `move` method).
slots = self.slots
weapon = slots[WieldLocation.TWO_HANDS]
if not weapon:
weapon = slots[WieldLocation.WEAPON_HAND]
if not weapon:
weapon = WeaponEmptyHand()
return weapon
```
In the `.armor()` method we get the item (if any) out of each relevant wield-slot (body, shield, head),
and grab their `armor` Attribute. We then `sum()` them all up.
In `.weapon()`, we simply check which of the possible weapon slots (weapon-hand or two-hands) have
something in them. If not we fall back to the 'fake' weapon `WeaponEmptyHand` which is just a 'dummy'
object that represents your bare hands with damage and all.
(created in [The Object tutorial](./Beginner-Tutorial-Objects.md#your-bare-hands) earlier).
## Extra credits
This covers the basic functionality of the equipment handler. There are other useful methods that
can be added:
- Given an item, figure out which equipment slot it is currently in
- Make a string representing the current loadout
- Get everything in the backpack (only)
- Get all wieldable items (weapons, shields) from backpack
- Get all usable items (items with a use-location of `BACKPACK`) from the backpack
Experiment with adding those. A full example is found in
[evennia/contrib/tutorials/evadventure/equipment.py](../../../api/evennia.contrib.tutorials.evadventure.equipment.md).
## Unit Testing
> Create a new module `mygame/evadventure/tests/test_equipment.py`.
```{sidebar}
See [evennia/contrib/tutorials/evadventure/tests/test_equipment.py](../../../api/evennia.contrib.tutorials.evadventure.tests.test_equipment.md)
for a finished testing example.
```
To test the `EquipmentHandler`, easiest is create an `EvAdventureCharacter` (this should by now
have `EquipmentHandler` available on itself as `.equipment`) and a few test objects; then test
passing these into the handler's methods.
```python
# mygame/evadventure/tests/test_equipment.py
from evennia.utils import create
from evennia.utils.test_resources import BaseEvenniaTest
from ..objects import EvAdventureRoom
from ..enums import WieldLocation
class TestEquipment(BaseEvenniaTest):
def setUp(self):
self.character = create.create_object(EvAdventureCharacter, key='testchar')
self.helmet = create.create_object(EvAdventureHelmet, key="helmet")
self.weapon = create.create_object(EvAdventureWeapon, key="weapon")
def test_add_remove):
self.character.equipment.add(self.helmet)
self.assertEqual(
self.character.equipment.slots[WieldLocation.BACKPACK],
[self.helmet]
)
self.character.equipment.remove(self.helmet)
self.assertEqual(self.character.equipment.slots[WieldLocation.BACKPACK], [])
# ...
```
## Summary
_Handlers_ are useful for grouping functionality together. Now that we spent our time making the
`EquipmentHandler`, we shouldn't need to worry about item-slots anymore - the handler 'handles' all
the details for us. As long as we call its methods, the details can be forgotten about.
We also learned to use _hooks_ to tie _Knave_'s custom equipment handling into Evennia.
With `Characters`, `Objects` and now `Equipment` in place, we should be able to move on to character
generation - where players get to make their own character!