About

This is an Entity-component-system implemented in Python. See the ECS FAQ for more info.

This implementation focuses on type-hinting, organization, and is designed to work well with Python. The following features are currently implemented:

• Entities can have store components which are instances of any Python object. Components are looked up by their type.
• Entities can have one instance of a type, or multiple instances of a type with a string or other hashable to differentiate them.
• Components can be registered as abstract, allowing a base type to hold subclasses of that component.
• Entity tags are distinct from components, tags are any hashable Python object rather than empty class.
• Entity relationships are supported, either as many-to-many or many-to-one relationships.
• ECS Queries can be made to fetch entities having a combination of components/tags/relations or the absence of such.

A lightweight version which implements only the entity-component framework exists called tcod-ec.

Installation

Use pip to install this library:

pip install tcod-ecs

If tcod is installed and the version is less than 14.0.0 then import tcod.ecs will fail. Remove or update tcod to fix this issue.

Examples

World

>>> import tcod.ecs
>>> world = tcod.ecs.World()  # New empty world

Entity

Each Entity is identified by its unique id (uid) which can be any hashable object and the world it belongs to. New unique entities can be created with World.new_entity which uses a new object() as the uid. An entity always knows about its assigned world. Worlds only know about their entities once the entity is assigned a name, component, tag, or relation.

>>> entity = world.new_entity()  # Creates a unique entity using `object()` as the uid
>>> entity
<Entity(uid=object at ...)>
>>> entity.world is world  # Worlds can always be accessed from their entity
True
>>> world[entity.uid] is entity  # Entities with the same world/uid are compared using `is`
True

# Reference an entity with the given uid, can be any hashable object:
>>> entity = world["MyEntity"]
>>> entity
<Entity(uid='MyEntity')>
>>> world["MyEntity"] is entity
True

Use World.new_entity to create unique entities and use World[x] to reference a global entity or relation with an id.

Serialization

Worlds are normal Python objects and can be pickled as long as all stored components can be pickled.

>>> import pickle
>>> pickled_data: bytes = pickle.dumps(world)
>>> world = pickle.loads(pickled_data)

Components

Components are instances of any Python type. These can be accessed, assigned, or removed from entities via the dict-like Entity.components attribute. The type is used as the key to access the component. The types used can be custom classes or standard Python types.

>>> import attrs
>>> entity = world.new_entity()
>>> entity.components[int] = 42
>>> entity.components[int]
42
>>> int in entity.components
True
>>> del entity.components[int]
>>> entity.components[int]  # Missing keys raise KeyError
Traceback (most recent call last):
  ...
KeyError: <Entity...>
>>> entity.components.get(int, "default")  # Test keys with `.get()` like a dictionary
'default'
>>> @attrs.define
... class Vector2:
...     x: int = 0
...     y: int = 0
>>> entity.components[Vector2] = Vector2(1, 2)
>>> entity.components[Vector2]
Vector2(x=1, y=2)
>>> entity.components |= {int: 11, Vector2: Vector2(0, 0)}  # Multiple values can be assigned like a dict
>>> entity.components[int]
11
>>> entity.components[Vector2]
Vector2(x=0, y=0)

# Queries can be made on all entities of a world with matching components
>>> for e in world.Q.all_of(components=[Vector2]):
...     e.components[Vector2].x += 10
>>> entity.components[Vector2]
Vector2(x=10, y=0)

# You can match components and iterate over them at the same time.  This can be combined with the above
>>> for pos, i in world.Q[Vector2, int]:
...     print((pos, i))
(Vector2(x=10, y=0), 11)

# You can include `Entity` to iterate over entities with their components
# This always iterates over the entity itself instead of an Entity component
>>> for e, pos, i in world.Q[tcod.ecs.Entity, Vector2, int]:
...     print((e, pos, i))
(<Entity...>, Vector2(x=10, y=0), 11)

Named Components

Only one component can be assigned unless that component is given a unique name. You can name components with the key syntax (name, type) when assigning components. Names are not limited to strings, and can be any hashable or frozen object. The syntax [type] and [(name, type)] can be used interchangeably in all places accepting a component key. Queries on components access named components with the same syntax and must use names explicitly.

>>> entity = world.new_entity()
>>> entity.components[Vector2] = Vector2(0, 0)
>>> entity.components[("velocity", Vector2)] = Vector2(1, 1)
>>> entity.components[("velocity", Vector2)]
Vector2(x=1, y=1)
>>> @attrs.define(frozen=True)
... class Slot:
...     index: int
>>> entity.components |= {  # Like a dict Entity.components can use |= to update items in-place
...     ("hp", int): 10,
...     ("max_hp", int): 12,
...     ("atk", int): 1,
...     str: "foo",
...     (Slot(1), str): "empty",
... }
>>> entity.components[("hp", int)]
10
>>> entity.components[str]
'foo'
>>> entity.components[(Slot(1), str)]
'empty'

# Queries can be made on all named components with the same syntax as normal ones
>>> for e in world.Q.all_of(components=[("hp", int), ("max_hp", int)]):
...     e.components[("hp", int)] = e.components[("max_hp", int)]
>>> entity.components[("hp", int)]
12
>>> for e, pos, delta in world.Q[tcod.ecs.Entity, Vector2, ("velocity", Vector2)]:
...     e.components[Vector2] = Vector2(pos.x + delta.x, pos.y + delta.y)
>>> entity.components[Vector2]
Vector2(x=1, y=1)

Tags

Tags are hashable objects stored in the set-like Entity.tags. These are useful as flags or to group entities together.

>>> entity = world.new_entity()
>>> entity.tags.add("player")  # Works well for groups
>>> "player" in entity.tags
True
>>> entity.tags.add(("eats", "fruit"))
>>> entity.tags.add(("eats", "meat"))
>>> set(world.Q.all_of(tags=["player"])) == {entity}
True

Relations

Use Entity.relation_components[component_key][target] = component to associate a relation with data. Use Entity.relation_tag[tag] = target to associate a tag exclusively with a target entity. Use Entity.relation_tags_many[tag].add(target) to associate a tag with multiple targets. Tags and relations share the same space then queried, so tags can not be in the format of a component key. Relations are unidirectional.

>>> @attrs.define
... class OrbitOf:  # OrbitOf component
...     dist: int
>>> LandedOn = "LandedOn"  # LandedOn tag
>>> star = world.new_entity()
>>> planet = world.new_entity()
>>> moon = world.new_entity()
>>> ship = world.new_entity()
>>> player = world.new_entity()
>>> moon_rock = world.new_entity()
>>> planet.relation_components[OrbitOf][star] = OrbitOf(dist=1000)
>>> moon.relation_components[OrbitOf][planet] = OrbitOf(dist=10)
>>> ship.relation_tag[LandedOn] = moon
>>> moon_rock.relation_tag[LandedOn] = moon
>>> player.relation_tag[LandedOn] = moon_rock
>>> set(world.Q.all_of(relations=[(OrbitOf, planet)])) == {moon}
True
>>> set(world.Q.all_of(relations=[(OrbitOf, ...)])) == {planet, moon}  # Get objects in an orbit
True
>>> set(world.Q.all_of(relations=[(..., OrbitOf, None)])) == {star, planet}  # Get objects being orbited
True
>>> set(world.Q.all_of(relations=[(LandedOn, ...)])) == {ship, moon_rock, player}
True
>>> set(world.Q.all_of(relations=[(LandedOn, ...)]).none_of(relations=[(LandedOn, moon)])) == {player}
True