[BUG] [PYTHON] additionalProperties not supported

Created by: ivan-gomes

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• What's the version of OpenAPI Generator used?
• Have you search for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Bounty to sponsor the fix (example)

Description

Generated Python clients do not have the ability to access the additional properties of models with additionalProperties defined. The only ones that can be accessed are those that are explicitly defined in the model and the rest are ignored. In contrast, the generated Java models extend HashMap when additionalProperties are defined and they can get accessed by Map#get(String).

openapi-generator version

4.0.0

OpenAPI declaration file content or url

  Element:
    type: "object"
    required:
    - "id"
    properties:
      id:
        type: "string"
      name:
        type: "string"
    additionalProperties:
      type: "object"

Full specification: https://github.com/Open-MBEE/mms/blob/develop/mms-ent/repo-amp/src/main/amp/web/mms/mms.swagger.yaml

Command line used for generation

java -jar /path/to/openapi-generator-cli.jar generate -i /path/to/mms.swagger.yaml -l python -o ~/tmp

Steps to reproduce

Inspecting the generated Element.py file after executing the command above with the specification above. There is also a usage of additionalProperties in the Petstore API that exhibits the same behavior.

Related issues/PRs

Clone of issue made and fixed in swagger-api/swagger-codegen: https://github.com/swagger-api/swagger-codegen/issues/8075

Suggest a fix

I believe that the additional properties can be stored in a dict, analogously to how they are handled in Java.