[BUG] [python-flask] [server] oneOf, anyOf Polymorphism does not work

[jethrogillgren]

Description

Same as #7414, but with python-flask.

oneOf or anyOf elements cause invalid python code generated.

Traceback (most recent call last):
  File "/usr/local/lib/python3.9/runpy.py", line 197, in _run_module_as_main
    return _run_code(code, main_globals, None,
  [...]
  File "/usr/src/app/openapi_server/controllers/default_controller.py", line 4, in <module>
    from openapi_server.models.one_of_cat_dog import OneOfCatDog  # noqa: E501
ModuleNotFoundError: No module named 'openapi_server.models.one_of_cat_dog'

openapi-generator version

4.3.1

OpenAPI declaration file content or url

openapi: "3.0.2"
info:
  version: 1.0.0
  title: Polymorphism
paths:
  /pets:
    post:
      requestBody:
        content:
          application/json:
            schema:
              oneOf:
                - $ref: '#/components/schemas/Cat'
                - $ref: '#/components/schemas/Dog'
              discriminator:
                propertyName: pet_type
      responses:
        '200':
          description: created
components:
  schemas:
    # Parent
    Pet:
      type: object
      required:
        - pet_type
      properties:
        pet_type:
          type: string
        eats:
          type: string
      discriminator:
        propertyName: pet_type
    # Child 1
    Dog:
      allOf:
        - $ref: '#/components/schemas/Pet'
        - type: object
          # all other properties specific to a `Dog`
          properties:
            bark:
              type: boolean
    # Child 2
    Cat:
      allOf:
        - $ref: '#/components/schemas/Pet'
        - type: object
          # all other properties specific to a `Cat`
          properties:
            climbs:
              type: boolean

Generation Details

docker run --rm -v ${PWD}:/local openapitools/openapi-generator-cli:v4.3.1 generate --input-spec /local/openapi.yaml --generator-name python-flask --output /local

Steps to reproduce

1. Run the above generation
2. docker build -t openapi_server .
3. docker run -p 8080:8080 openapi_server

Related issues/PRs

#6815
#5565
#7789

Thanks!