[BUG][PYTHON-CLIENT] Generated Imports Do Not Respect Custom Folder Names Set via --additional-properties

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

When generating a Python client with OpenAPI Generator, the generated import paths do not respect the custom folder names set via --additional-properties (e.g., modelPackage=dto, apiPackage=service). Although some imports correctly use the custom folder names, others incorrectly reference the default folder names (models and service), leading to inconsistencies and potential import errors.

Examples of incorrect and correct imports:

• In the generated init.py APIs are incorrectly imported as
  from service.fake_api import FakeApi
  Instead of the expected
  from openapi_client.service.fake_api import FakeApi.

• However, in the same file, model imports are correctly generated
  from openapi_client.dto.api_response import ApiResponse.

• In other files, such as pet_api.py, models are incorrectly imported from the default modules folder, instead of the specified dto folder from openapi_client.models.api_response import ApiResponse.

Expected Behaviour

The generator should consistently apply the modelPackage and apiPackage folder names across all imports, avoiding mismatches between expected and generated imports.

openapi-generator version

7.11.0

OpenAPI declaration file content or url

OpenAPI's Generator petstore api examples:

Command line used for generation

docker run --rm
-v ${PWD}:/local openapitools/openapi-generator-cli generate
-i /local/apis/petstore.yml
-g python
--additional-properties=sourceFolder=,modelPackage=dto,apiPackage=service
-o /local/generated-docker

Steps to reproduce

running the command line on the specified api

Related issues/PRs

A full example, including generated code and expected output, can be found here: https://github.com/claudiadpp/openapi-python-demo/pull/1

• Generated Code (Incorrect Imports): View Here
• Expected Output (Fixed Imports): View Here

Suggest a fix

Start by running the reported Docker generation command with the petstore API and custom modelPackage=dto and apiPackage=service values. Inspect the generated init.py and pet_api.py files, comparing their imports with the linked expected output. Done means all generated imports consistently use the configured folder names without references to default modules.