fractal-specifications 1.0.2

Fractal Specifications is an implementation of the specification pattern for building SOLID logic for your Python applications.

Fractal Specifications

Fractal Specifications is an implementation of the specification pattern for building SOLID logic for your Python applications.

Installation

pip install fractal-specifications

Development

Setup the development environment by running:

make deps

Happy coding.

Occasionally you can run:

make lint

This is not explicitly necessary because the git hook does the same thing.

Do not disable the git hooks upon commit!

Usage

Specifications can be used to encapsulate business rules. An example specification is EqualsSpecification("maximum_speed", 25).

A specification implements the is_satisfied_by(obj) function that returns True or False, depending on the state of the obj that is passed into the function as parameter. In our example, the obj needs to provide the attribute maximum_speed.

Full code example

This example includes a repository to show an application of specifications.

from abc import ABC, abstractmethod
from dataclasses import dataclass
from typing import List

from fractal_specifications.generic.operators import EqualsSpecification
from fractal_specifications.generic.specification import Specification


@dataclass
class Road:
    maximum_speed: int

    @staticmethod
    def slow_roads_specification():
        return EqualsSpecification("maximum_speed", 25)


class RoadRepository(ABC):
    @abstractmethod
    def get_all(self, specification: Specification) -> List[Road]:
        ...

    def slow_roads(self) -> List[Road]:
        return self.get_all(Road.slow_roads_specification())


class PythonListRoadRepository(RoadRepository):
    def __init__(self, roads: List[Road]):
        self.roads = roads

    def get_all(self, specification: Specification) -> List[Road]:
        return [
            road for road in self.roads
            if specification.is_satisfied_by(road)
        ]


road_repository = PythonListRoadRepository([
    Road(maximum_speed=25),
    Road(maximum_speed=50),
    Road(maximum_speed=80),
    Road(maximum_speed=100),
])


if __name__ == '__main__':
    print(road_repository.slow_roads())