[BUG][Python] date-time default value is ignored in python-legacy client

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

With the python-legacy generator, a default value set on a string field with a date-time format is ignored in the generated python client.

openapi-generator version

v6.0.0 (and latest)

OpenAPI declaration file content or url

openapi: 3.0.0
info:
  description: test
  version: 0.0.0
  title: test
servers:
  - url: /api
paths:
  /collector/v1/packages_block:
    post:
      operationId: postPackagesBlock
      requestBody:
        content:
          application/json:
            schema:
              "$ref": '#/components/schemas/PackagesBlock'
      responses:
        200:
         description: Successful request
components:
  schemas:
    PackagesBlock:
      type: object
      properties:
        package:
          "$ref": '#/components/schemas/PackagesBlockPackage'
    PackagesBlockPackage:
      type: object
      properties:
        installation_date:
          type: string
          format: date-time
          description: Date and time of package installation.
          example: "1995-08-22T05:08:28Z"
          default: "1995-08-22T05:08:28Z"

Generation Details

docker run --rm openapitools/openapi-generator-cli:latest generate \
	--input-spec /specification/openapi.yml \
	--generator-name python-legacy \
	--library asyncio \
	--package-name  ${CLIENT_PACKAGE_NAME} \
	--additional-properties packageName=${CLIENT_PACKAGE_NAME} \
	--additional-properties packageVersion=${CLIENT_VERSION} \
	--output ${GENERATED_CLIENT}

Steps to reproduce

1. Execute openapitools/openapi-generator-cli:latest generate on the provided specification

2. Check the generated PackagesBlockPackage client model and focus on the __init__ method:

   class PackagesBlockPackage(object):
       # [...]
   
       def __init__(self, installation_date=None, local_vars_configuration=None):  # noqa: E501
           """PackagesBlockPackage - a model defined in OpenAPI"""  # noqa: E501
           if local_vars_configuration is None:
               local_vars_configuration = Configuration.get_default_copy()
           self.local_vars_configuration = local_vars_configuration
   
           self._installation_date = None
   
           self.installation_date = installation_date
   

Notice that the installation_date parameter of PackagesBlockPackage.__init__ is defaulted to Null instead of 1995-08-22T05:08:28Z.

Related issues/PRs

N/A

Suggest a fix

In progress. I'll do my best without Java knowledge.

Start by running the provided OpenAPI specification with the python-legacy generator and asyncio library, then inspect the generated PackagesBlockPackage.__init__ method. Compare the installation_date default with the declared date-time value; done means the generated client preserves that default instead of using null.