What are the signs indicating the use of hexagonal architecture in the code?

Hexagonal architecture (or Ports and Adapters) is characterized by the following features:

• Clear separation between the core and external interfaces. The application core contains business logic and does not depend on external systems.
• Use of ports and adapters. Ports are interfaces through which the core interacts with the outside world, and adapters are specific implementations of these interfaces.
• No direct dependencies of the core on infrastructure. For example, business logic does not depend on databases, UI, or network protocols.
• Testability. Thanks to the isolation of business logic, it is easy to write unit tests by mocking adapters.

Example in Python:

from abc import ABC, abstractmethod

# Port (interface)
class UserRepository(ABC):
    @abstractmethod
    def get_user(self, user_id: int):
        pass

# Application core
class UserService:
    def __init__(self, user_repo: UserRepository):
        self.user_repo = user_repo

    def get_user_name(self, user_id: int) -> str:
        user = self.user_repo.get_user(user_id)
        return user.name

# Adapter (concrete implementation of the port)
class InMemoryUserRepository(UserRepository):
    def __init__(self):
        self.users = {1: type('User', (), {'name': 'Alice'})()}

    def get_user(self, user_id: int):
        return self.users.get(user_id)

# Usage
repo = InMemoryUserRepository()
service = UserService(repo)
print(service.get_user_name(1))  # Alice

In this example, the business logic (UserService) does not depend on the specific storage implementation (InMemoryUserRepository). This is a characteristic of hexagonal architecture.