example.py

class ActivationCode:  # facultatif
  pass


class ActivationCodeGeneratorInterface:
  def generate(self, key: str, counter: int, duration_days: int) -> ActivationCode:
    raise NotImplementedError


class RESTAPI:
  def __init__(self, code_generator: ActivationCodeGeneratorInterface) -> None:
    self.code_generator = code_generator
  
  def generate(self, request) -> Response:
    return Response.JSON({
      'activation_key': self.code_generator.generate(request.key, request.counter, request.duration_days),
    })
  
  def run(self) -> None:
    pass


class OpenPAYGOActivationCodeGenerator(ActivationCodeGeneratorInterface):
  def generate(self, key, counter: int, duration_days: int) -> ActivationCode:
    openpaygolib.generate_token(key, counter, duration_days)


class FakeActivationCodeGenerator(ActivationCodeGeneratorInterface):
  def generate(self, key, counter: int, duration_days: int) -> ActivationCode:
    return 123456

# app/settings.py

CODE_GENERATOR_MODULE = env.str('CODE_GENERATOR_MODULE', 'OpenPAYGO')

# app/__init__.py

code_generator: ActivationCodeGeneratorInterface
if settings.CODE_GENERATOR_MODULE = 'OpenPAYGO':
  code_generator = OpenPAYGOActivationCodeGenerator()
elif settings.CODE_GENERATOR_MODULE = 'fake':
  code_generator = FakeActivationCodeGenerator()
else:
  raise ValueError(f"CODE_GENERATOR_MODULE setting not valid")

rest_api = RESTAPI(code_generator=code_generator)

# start.py

import app

app.rest_api.run()