[Python] Recursive/Cyclic definitions cause import error in Python-experimental

Created by: eak24

The problem is that with the changes to have the class property types used directly, circular type referencing or recursive definitions doesn't seem to work anymore:

OpenAPI declaration file content or url

components:
  schemas:
    Dog:
      properties:
        enemy:
          type: object
          $ref: '#/components/schemas/Dog'

This should be a valid spec, but the generated python attempts to reference the Dog class in the definition of the Dog class - which clearly doesn't work. This causes a circular import. This looks to be a regression from just the plain python generator - which uses strings to define openApi types. What are your thoughts on this?

Command line used for generation

Normal generation for python-experimental using any spec which has a circular reference.

Steps to reproduce

Make a spec with a circular reference, run the python-experimental generator, attempt to use the client, and you'll get an import error.

Related issues/PRs

This started happening with #4446 .

Suggest a fix

@spacether suggested simply storing a model's parameter types as a class method rather than a dict. Then they will not be loaded at module load time.