Simple Dependency Injection in Python

DI.py

# I'm using Django models as inspiration in this example
from mymodels import User, Org

# You could also call these Getters or DAOs etc
# The point is that they perform some kind of 
# side effect like talking to a DB or an API

@dataclass(frozen=True)
class UserConnector:
  def get_user(id: str) -> User:
    return User.objects.get(id=id)
  
@dataclass(frozen=True)
class OrgConnector:
  def get_org(id: str) -> Org:
    return Org.objects.get(id=id)
  
# Service is a collection of business logic 
# that we want to have Dependency Injection support 

# By injecting all the Connectors, 
# we have good separation of concerns 
# and testing becomes simple

@dataclass(frozen=True)
class UserService:
  # We can pass in the default implementations here and 
  # replace them in tests or if we do a UserService V2
  # that coexists with V1 but has different Connectors.
  user_connector: UserConnector = UserConnector()
  org_connector: OrgConnector = OrgConnector()
  
  def get_user_with_org(self, id: str) -> User:
    return {
        'user': self.user_connector.get_user(id),
        'org': self.org_connector.get_org(id)
    }

if __name__ == '__main__':
    # can be parametrised with Mock user_connector and org_connector
    s = UserService()
    user = s.get_user_with_org("123")