[BUG] [PythonFlask] TypeError traceback (petshop.yaml)

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• What's the version of OpenAPI Generator used?
• Have you search for related issues/PRs?
• What's the actual output vs expected output?
• [Optional] Bounty to sponsor the fix (example)

Description

New installation will not create a working Flask container from the generated Dockerfile when I generate python-flask server from the demo modules/openapi-generator/src/test/resources/3_0/petstore.yaml in this repo. I get TypeError: Failed to fetch within the v2/ui, and a different TypeError with stacktrace in the log.

openapi-generator version

Master or 3.3.4

OpenAPI declaration file content or url

The petstore.yaml contained in test directory of this repo.

Command line used for generation

generate -i openapi-generator/modules/openapi-generator/src/test/resources/3_0/petstore.yaml -g python-flask -o new

or
run the openapi-generator-online image from dockerhub at local fqdn as noted below.

Steps to reproduce

1. create a vhost/ingress openapi-gen and launch the generator, e.g. docker run -p 80:8080 -d openapitools/openapi-generator-online:v3.3.4 (I did the equivalent with k8s)
2. generate a python-flask petstore

GENERATOR_FQDN=openapi-gen.$MYDOMAIN
sudo apt install jq unzip
curl -o flask.zip \
  $(curl -s -X POST --header 'Content-Type: application/json' \
    --header 'Accept: application/json' \
    -d '{"openAPIUrl": "https://raw.githubusercontent.com/openapitools/openapi-generator/master/modules/openapi-generator/src/test/resources/3_0/petstore.yaml"}' \
    http://$GENERATOR_FQDN/api/gen/servers/python-flask \
    | jq -r .link)
unzip flask.zip
cd python-flask-server
sed -i -e "s/petstore.swagger.io/$(hostname -f):8080/" openapi_server/openapi/*.yaml
docker build . -t  petshop
docker run -p 8080:8080 --name=petshop -d petshop

3. Then try to invoke actions such as

curl -X POST "http://$(hostname -f):8080/v2/user" -H "accept: */*" -H "Content-Type: application/json" -d "{\"email\":\"email@foo.com\",\"firstName\":\"firstName\",\"id\":0,\"lastName\":\"lastName\",\"password\":\"password\",\"phone\":\"phone\",\"userStatus\":6,\"username\":\"myname\"}"

On backend I see logs that look like:

192.168.2.44 - - [19/Feb/2019 06:54:17] "OPTIONS /v2/user HTTP/1.1" 200 -
[2019-02-19 06:54:31,738] ERROR in app: Exception on /v2/user [POST]
Traceback (most recent call last):
  File "/usr/local/lib/python3.7/site-packages/flask/app.py", line 2292, in wsgi_app
    response = self.full_dispatch_request()
  File "/usr/local/lib/python3.7/site-packages/flask/app.py", line 1815, in full_dispatch_request
    rv = self.handle_user_exception(e)
  File "/usr/local/lib/python3.7/site-packages/flask/app.py", line 1718, in handle_user_exception
    reraise(exc_type, exc_value, tb)
  File "/usr/local/lib/python3.7/site-packages/flask/_compat.py", line 35, in reraise
    raise value
  File "/usr/local/lib/python3.7/site-packages/flask/app.py", line 1813, in full_dispatch_request
    rv = self.dispatch_request()
  File "/usr/local/lib/python3.7/site-packages/flask/app.py", line 1799, in dispatch_request
    return self.view_functions[rule.endpoint](**req.view_args)
  File "/usr/local/lib/python3.7/site-packages/connexion/decorators/decorator.py", line 73, in wrapper
    response = function(request)
  File "/usr/local/lib/python3.7/site-packages/connexion/decorators/uri_parsing.py", line 132, in wrapper
    response = function(request)
  File "/usr/local/lib/python3.7/site-packages/connexion/decorators/validation.py", line 165, in wrapper
    response = function(request)
  File "/usr/local/lib/python3.7/site-packages/connexion/decorators/decorator.py", line 44, in wrapper
    response = function(request)
  File "/usr/local/lib/python3.7/site-packages/connexion/decorators/parameter.py", line 126, in wrapper
    return function(**kwargs)
TypeError: create_user() missing 1 required positional argument: 'user'

I also tried the older resources/2_0/petstore.yaml and ran into TypeError: cannot convert dictionary update sequence element #0 instead of the positional-argument error.

Related issues/PRs

I cannot find one here or by googling the error messages, so that's why I'm here. Closest thing I can find is unresolved issue #1666.

Suggest a fix

I'm a newbie to this (though I do have some familiarity with swagger/flask/etc), and it looks to me like a getting-started.md with full examples (validated by the CI so they don't break) would help greatly.

Reproduce the issue with modules/openapi-generator/src/test/resources/3_0/petstore.yaml using the python-flask generator, then inspect the generated openapi_server and the create_user traceback. Compare the 3_0 and 2_0 petstore outputs and run the Docker build and POST /v2/user request. Done means the generated Flask container handles the request without a TypeError.