elda27 / finjet

Simple dependency injection library like fastapi

finjet

Simple dependency injection library like fastapi. It can be used to turn your modules to loosely coupled parts. and configurations to allow you to easily re-use and test your code.

Dependency injection is performed on the arguments given with the Depends function as the default argument. The inserted value will be given values of NamedTuple via Container.configure or the return value of the function.

Installation

Latest PyPI stable release

pip install finjet

Example

from typing import NamedTuple
from finjet import Container, Depends, Singleton, inject


class Config(NamedTuple):
    gear_ratio: int
    tire_r: int = 100


class Engine:
    # gear_ratio will be obtained from `Config`
    def __init__(self, gear_ratio: int = Depends()) -> None:
        self.gear_ratio = gear_ratio


class Tire:
    count = 0

    def __init__(self, tire_r: int = Depends()) -> None:
        Tire.count += 1
        # Actually tire_r is multiplied by instanced number of times.
        self.tire_r = tire_r * Tire.count


def get_rotation_speed(engine: Engine = Depends(Engine)) -> int:
    # Arguments of `Engine` class will inject from dependencies.
    # In this example, the gear_ratio is configured 100 or 50
    return engine.gear_ratio


@inject
def get_tire_speed(
    tire: Tire = Singleton(Tire),
    rpm: int = Depends(get_rotation_speed)
) -> float:
    # Depends is always created such as factory pattern
    # Singleton is only generate at once such as singleton pattern.
    # The singleton object is shared in the Container class.
    return tire.tire_r * rpm


def main():
    container = Container()

    # Configuration of container
    container.configure(Config(100, 100))
    with container:
        print('Speed:', get_tire_speed())  # 10000
        print('#Tire:', Tire.count)  # 1

    # If the configuration value is changed, the displaying value is difference.
    # But `Tire.count` is same so that a second argument, the Tire object is re-used.
    container.configure(Config(20, 100))
    with container:
        print('Speed:', get_tire_speed())  # 2000
        print('#Tire:', Tire.count)  # 1

    # If the configuration value is changed, the displaying value is difference.
    # The `Tire` object is updated.
    container.configure(Config(20, 10))
    with container:
        print('Speed:', get_tire_speed())  # 400
        print('#Tire:', Tire.count)  # 2


if __name__ == '__main__':
    main()