Minimal dependency injection container for Python. Provides immutable rule definitions, singleton/transient lifetimes, scoped caching, nested attribute resolution, cycle detection, and optional validation, logging, and ordering layers.
How to use it
Installation
pip install doppy-di
Requires Python 3.10 or later.
Basic usage
from doppy_di.container import ContainerBuilder
builder = ContainerBuilder()
# Register a singleton service
builder.service("answer", lambda: 42, lifetime="singleton")
# Register a transient service with dependencies
builder.service("greeting", lambda name: f"Hello, {name}!", deps=["name"])
builder.value("name", "World")
container = builder.build()
print(container.get("answer")) # 42
print(container.get("greeting")) # Hello, World!
Scoped caching
with container.scope("request") as scope:
a = scope.get("greeting")
b = scope.get("greeting")
assert a is b # cached within scope
# scope cache is cleared on exit
Override for testing
with container.override("answer", 99):
print(container.get("answer")) # 99
print(container.get("answer")) # restored to 42
Use cases
Service registration with dependency injection
Register factories with explicit lifetime and dependency list. Container resolves the dependency graph on first access.
builder.service("db", lambda: Database("sqlite:///app.db"), lifetime="singleton")
builder.service("repo", lambda db: Repository(db), deps=["db"])
container = builder.build()
repo = container.get("repo")
Value objects and constants
Inject pre-computed values or configuration objects.
builder.value("config", {"debug": True, "port": 8080})
container.get("config") # {"debug": True, "port": 8080}
Aliasing
Create an alias that delegates resolution to another key.
builder.service("real_service", lambda: Service(), lifetime="singleton")
builder.alias("service", "real_service")
assert container.get("service") is container.get("real_service")
Nested attribute resolution
Access nested attributes of resolved services using tuple keys.
builder.service("db", lambda: Database("prod"), lifetime="singleton")
# resolve db.connection directly
container.get(("db", "connection")) # returns db.connection
Scoped request context
Use named scopes for per-request caching without polluting the global singleton cache.
def handle_request(request_id: str) -> dict:
with container.scope(request_id) as scope:
user = scope.get("current_user")
data = scope.get("request_data")
return process(user, data)
Validation at build time
Enable build-time validation to catch missing dependencies early.
builder.service("a", lambda b: A(b), deps=["b"])
try:
container = builder.build(validate=True)
except ContainerBuildError as e:
print(e.missing) # [("a", "b")]
Duplicate key policy
Control behaviour on duplicate registration.
from doppy_di.container import DuplicateKeyPolicy
strict = ContainerBuilder(duplicate_policy=DuplicateKeyPolicy.FAIL)
strict.service("x", lambda: 1)
strict.service("x", lambda: 2) # raises DuplicateKeyError
warning = ContainerBuilder(duplicate_policy=DuplicateKeyPolicy.WARN)
warning.service("x", lambda: 1)
warning.service("x", lambda: 2) # logs warning, overwrites
Optional runtime layers
The devkit package provides optional extensions:
from doppy_di.devkit import LoggingContainer, ValidatingContainer
container = LoggingContainer(container) # log all get operations
container = ValidatingContainer(container) # validate before resolving
from doppy_di.devkit.nested import NestedRules, SameValuePolicy
nested = NestedRules()
nested.add_rule("parent", "child", SameValuePolicy())
from doppy_di.devkit import ChildrenFirstPolicy, ParentFirstPolicy
from doppy_di.devkit.policy import OrderPolicy
# control the order of nested field resolution
policy = ChildrenFirstPolicy()
Additional information can be found in Documentation.
How to contribute
- Fork the repository.
- Create a feature branch (
git checkout -b feat/my-feature). - Install development dependencies:
uv sync --extra dev. - Make changes. Format and lint with:
uv run ruff format . && uv run ruff check --fix . - Type-check:
uv run mypy. - Run tests:
uv run pytest. - Commit messages must follow Conventional Commits (enforced via commitlint).
- Open a pull request against
main.
1 maintainer
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