[PYTHON] multipart/form-data syntaxe for codegen

Description

When running swagger-codegen-v3 from docker for post.

post:
    summary: Create something
    operationId: createSomething
    requestBody:
      required: true
      content:
        multipart/form-data:
          schema:
            allOf:
              - $ref: '#/components/schemas/SomethingProperties'
              - type: object
                properties:
                  file:
                    type: array
                    items:
                      type: string
                      format: binary

Does not produce the body for method create_something. By replacing multipart/form-data by multipart/formdata, the correct body model is added as argument for create_something. But does not send the files by giving a file path.

    def create_something(self, body, **kwargs):  # noqa: E501
        """
        :param async_req bool
        :param Body1 body: (required)
        :return: InlineResponse2004
                 If the method is called asynchronously,
                 returns the request thread.
        """
        kwargs['_return_http_data_only'] = True
        if kwargs.get('async_req'):
            return self.create_something_with_http_info(body, **kwargs)  # noqa: E501
        else:
            (data) = self.create_something_with_http_info(body, **kwargs)  # noqa: E501
            return data

Usage:

from __future__ import print_function
import app_pyclient
from app_pyclient.models import Body1, SomethingProperties
from app_pyclient.rest import ApiException
from pprint import pprint
import app_pyclient

configuration = app_pyclient.Configuration()
api_instance = app_pyclient.SomethingApi(app_pyclient.ApiClient(configuration))
try:
    file = 'path/to/a/file'
    payload = {'something_arg_1': 'value'}
    body = Body1([file,], **payload)
    api_response = api_instance.create_something(body=body)
    pprint(api_response)
except ApiException as e:
    print(e)

response: Cannot prepare a request message for provided arguments. Please check that your arguments match declared content type.

Swagger-codegen version

3.0.25
docker pull swaggerapi/swagger-codegen-cli-v3:3.0.25

Command line used for generation

docker run --rm -v "${PWD}:/local" swaggerapi/swagger-codegen-cli-v3:3.0.25 generate -i /local/my-specification.yaml -DpackageName=mypackage -l python -o /local/out/python

Steps to reproduce

Run the sample code provided.
Error message: Cannot prepare a request message for provided
arguments. Please check that your arguments match
declared content type.

Related issues/PRs

Suggest a fix/enhancement

Reproduce the issue with the provided OpenAPI schema using swagger-codegen 3.0.25 and the Python generator. Compare the generated create_something method and request handling for multipart/form-data versus multipart/formdata; done means the standard content type generates a usable body and successfully sends a file path.