How to Apply the Clean Architecture Dependency Rule in Python

from dataclasses import dataclass
from typing import List, Protocol

class Repository(Protocol):
    def get_items(self) -> List[str]:
        ...

@dataclass
class InMemoryRepository:
    items: List[str]

    def get_items(self) -> List[str]:
        return self.items

class UseCase:
    """Application layer depends on interfaces, not implementations."""
    def __init__(self, repository: Repository):
        self.repository = repository

    def execute(self) -> List[str]:
        return [item.upper() for item in self.repository.get_items()]

class ConsolePresenter:
    """Interface layer depends on application and domain layers."""
    def present(self, items: List[str]) -> None:
        print(f"Items: {', '.join(items)}")

def main():
    # Composition root: wires dependencies
    repository = InMemoryRepository(items=["apple", "banana", "cherry"])
    usecase = UseCase(repository)
    presenter = ConsolePresenter()

    # Presenter calls usecase, usecase calls repository
    presenter.present(usecase.execute())

if __name__ == "__main__":
    main()