Simple, type-safe dependency injection in idiomatic Python, inspired by FastAPI.
from injected import depends, resolver
def get_a() -> int:
return 13
def get_b() -> int:
return 17
@resolver
def get_sum(
a: int = depends(get_a),
b: int = depends(get_b),
) -> int:
return a + b
assert get_sum() == 30
It's sometimes useful to be able to provide an already resolved value, making it available throughout the dependency graph. The canonical example of this is how FastAPI makes things like requests and headers available to all dependencies.
To use this pattern, you specify a sentinel function, get_global_value
in the example
below, and then map it to a resolved value in a context passed to seed_context()
.
from injected import depends, resolver, seed_context
def get_global_value() -> int: ...
@resolver
def calculate_value(a: int = depends(get_global_value)) -> int:
return a + 13
seeded = seed_context(calculate_value, {get_global_value: 31})
assert seeded() == 44
Dependencies can be any combination of async and non-async functions and context managers. Async dependencies are resolved concurrently, and are scheduled at the optimal time, as soon as their own dependencies are resolved.
Context managers are torn down upon exiting the entry-point function.
import asyncio
from collections.abc import AsyncIterator
from contextlib import asynccontextmanager
from injected import depends, resolver
async def get_a() -> int:
return 13
def get_b() -> int:
return 17
@asynccontextmanager
async def get_c() -> AsyncIterator[int]:
yield 23
@resolver
async def get_sum_async(
a: int = depends(get_a),
b: int = depends(get_b),
c: int = depends(get_c),
) -> int:
return a + b + c
@resolver
def get_sum_sync(
a: int = depends(get_a),
b: int = depends(get_b),
c: int = depends(get_c),
) -> int:
return a + b + c
assert asyncio.run(get_sum_async()) == 53
assert get_sum_sync() == 53