tiny-fastapi-di

Production-ready async dependency injection in ~220 lines. FastAPI-compatible patterns, minimal code, no hidden complexity.

Installation

pip install tiny-fastapi-di

# With Pydantic validation
pip install tiny-fastapi-di[pydantic]

Quick Start

from tiny_fastapi_di import Depends, empty_di_ctx

def get_db():
    return "database_connection"

async def get_user(db: str = Depends(get_db)):
    return f"User from {db}"

# One call handles context and cleanup
result = await empty_di_ctx.call_fn(get_user)

Why tiny-fastapi-di?

• Production-ready: ~220 lines of auditable code. No hidden complexity.
• Familiar API: Same Depends() pattern as FastAPI
• Framework-agnostic: Use in CLI tools, workers, pipelines, anywhere
• Correct by default: Cleanup runs automatically, circular dependencies detected

Core Features

from typing import Annotated
from tiny_fastapi_di import Depends, empty_di_ctx

# Basic dependency
async def endpoint(db = Depends(get_db)): ...

# Annotated syntax
async def endpoint(db: Annotated[DB, Depends(get_db)]): ...

# Infer callable from type
async def endpoint(db: Annotated[DB, Depends()]): ...

# Disable caching
async def endpoint(db = Depends(get_db, use_cache=False)): ...

# Yield dependencies with automatic cleanup
def get_db():
    db = connect()
    try:
        yield db
    finally:
        db.close()

Value Injection

result = await empty_di_ctx.call_fn(my_endpoint, request_id=123, user_id=456)

Dependency Substitution (Testing)

result = await empty_di_ctx.call_fn(
    my_endpoint,
    fn_map={real_db: mock_db}
)

Pydantic Validation

from tiny_fastapi_di.pydantic import pydantic_di_ctx

async def endpoint(user: User):  # User is a Pydantic model
    return user

result = await pydantic_di_ctx.call_fn(endpoint, user={"name": "Alice", "age": 30})

Feature Comparison

Feature	FastAPI	tiny-fastapi-di
Depends()	✅	✅
Depends(use_cache=False)	✅	✅
Annotated[T, Depends()]	✅	✅
yield dependencies	✅	✅
Async dependencies	✅	✅
Circular detection	❌	✅
Value injection	❌	✅
Dependency substitution	partial	✅
Optional validation	❌	✅

License

MIT