[BUG] [PYTHON] Generated class methods without self parameter

Created by: gcatanese

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?
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Description

When generating the Python client code the class methods do not have self parameter

openapi-generator version

Occurring with v6.0.1-SNAPSHOT

OpenAPI declaration file content or url

openapi: 3.0.3
info:
  description: API with post endpoint
  termsOfService: n/a
  title: API spec
  version: "12"
servers:
- url: http://localhost:8080
tags:
- name: Modifications
paths:
  /postEndpoint:
    get:
      operationId: postEndpoint
      parameters:
      - explode: true
        in: query
        name: options
        required: false
        schema:
          $ref: '#/components/schemas/Options'
        style: deepObject
      responses:
        "200":
          content:
            text/plain:
              schema:
                type: string
          description: OK
components:
  schemas:
    Options:
      properties:
        a:
          format: date-time
          nullable: true
          type: string
        b:
          format: date-time
          nullable: true
          type: string
        c:
          items:
            type: string
          type: array
      type: object

Generation Details

Generated with

java -jar openapi-generator-cli/target/openapi-generator-cli.jar generate \
   -i openapi.yaml \
   -g python \
    -p packageName=checkout \
    -o src

Steps to reproduce

Run the command above

Related issues/PRs

See #12560

Suggest a fix