[BUG] [Python] Model initialization does not accept iterable postitional arguments

Created by: ckoegel

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?
• [Optional] Sponsorship to speed up the bug fix or feature request (example)

Description

When generating models from openapi schemas, these objects do not accept iterable objects for initializing new instances. The init function accepts both *args and **kwargs, but the file invalid_pos_args.mustache causes an ApiTypeError if any *args are passed in.

openapi-generator version

0.5.3

OpenAPI declaration file content or url

https://github.com/OpenAPITools/openapi-generator/blob/master/modules/openapi-generator/src/main/resources/python/model_templates/invalid_pos_args.mustache https://github.com/OpenAPITools/openapi-generator/blob/master/modules/openapi-generator/src/main/resources/python/model_templates/model_normal.mustache

Generation Details

using the spec at https://github.com/Bandwidth/api-docs/blob/main/site/specs-source/messaging.json and generating using openapi-generator-cli generate -g python -i messaging.json -o ./msg-test allows for viewing the generated SDK,

Steps to reproduce

After generating, attempting to create a BandwidthCallbackMessage by passing in a dict, ex: BandwidthCallbackMessage(my_dict) causes the ApiTypeError "Invalid positional arguments...". This can be avoided by using **kwargs, ex: BandwidthCallbackMessage(**my_dict), but since the message attribute is also an object (BandwidthMessage), the same issue arises, nested in the creation of BandwidthCallbackMessage, and the error is thrown anyway.

Related issues/PRs

None

Suggest a fix

By creating the instance of BandwidthCallbackMessage using BandwidthCallbackMessage(**my_dict), and then putting the code below inside the for var_name, var_vlaue in kwargs.items(): loop inside the init function of the generated model file, I was able to generate both objects successfully.

if var_name not in self.attribute_map and \
                        self._configuration is not None and \
                        self._configuration.discard_unknown_keys and \
                        self.additional_properties_type is None:
                # discard variable.
                continue
            if var_name == "message":
                setattr(self, var_name, BandwidthMessage(**var_value))
            else:
                setattr(self, var_name, var_value)
            if var_name in self.read_only_vars:
                raise ApiAttributeError(f"`{var_name}` is a read-only attribute. Use `from_openapi_data` to instantiate "
                                     f"class with read only attributes.")

This solution is honestly horrendous and only works for this very specific use case, but shows that it can be done. I will be attempting to modify the logic inside the if args: statement in the same file to recursively check for objects in the args field and convert them to kwargs to be set normally. This solution should allow for a much more standardized solution to the issue. I'll be making a PR with my progress on this.