Python connexion not displaying Swagger UI

Question

I've built a Python/Flask based REST API using the connexion module. This working well as defining the REST API with with swagger.yml file works very well. The application is running, but when I navigate to /ui all I get in my browser is this:

I haven't disabled the UI, so I'm not sure what's going on and why the UI isn't being displayed. My application doesn't have a /static folder (it's only an API), so the app isn't serving any static files, not sure if that's related to the problem or not.

Any suggestions, pointers or hints about what I'm doing wrong would be most appreciated!

Here is a simplified example of my code:

# 3rd party libraries
from flask_cors import CORS
import connexion

def create_app(config_key, instance_config=None):
    # create the connexion instance
    connex_app = connexion.FlaskApp(__name__, specification_dir='./files/swagger/')
    connex_app.server = 'gevent'

    # get the Flask app instance
    app = connex_app.app

    # configure the application
    app.config.from_object(config_key)

    # add CORS support to application
    CORS(app)

    # define the API with the SWAGGER API definition YAML file
    connex_app.add_api('line_controller_api.yml',
                       base_path='{url_prefix}'.format(url_prefix=app.config.get('URL_PREFIX', '/')),
                       resolver=AppResolver())

    return connex_app


def production_app(instance_config=None):
    app = create_app('api_config.ProductionConfig', instance_config)
    return app

if __name__ == '__main__':
    app = create_app('api_config.DevelopmentConfig')
    port = 5001
    logger.info('Line Controller API running on port %s', port)
    app.run(host='0.0.0.0', port=port)

Thanks in advance, Doug

Answer 1

connexion from 2.0.1 version onward don't have swagger-ui bundled inside it. You have install it explicitly using the below command (note the quotes)

pip install 'connexion[swagger-ui]'

Once you install it. swagger will work with connexion. In the earlier version swagger used to work with /ui added to your url at the end http(s)://host:port

But in 2.0.x onward use http(s)://host:port/<basepath>/ui

Answer 2

My stackoverflow reputation is too low for me to comment on Ashraff Ali Wahab 's answer above but I just found out that I can edit it myself. Suffice it to say that it fixed the problem for me after I understood that the shell syntax, as presented, is wrong which was pointed out by Pablo Marin-Garcia . This is the shell syntax you need in Unix/Linux to properly install the swagger-ui plugin:

pip install 'connexion[swagger-ui]'

Any matched quotes will do. Note well that without the quotes, the pip command will run successfully but it won't install the swagger-ui component as you expect it to. Furthermore, I spent a lot of time scratching my head on this one because I did this in a virtualenv. I also searched the virtualenv for the swagger-ui component with find and I found some stub installed. So, if you are new to python or you are in a hurry, this can be easy to miss.

At the end of the day, I decided to add a local_requirement.txt file listing the correct version of Werzueg, connexion, and "connexion[swagger-ui]" which I install before using the stock requirements.txt because it seems like the Flask API code generated by the SmartBear tools is a little dated.

Answer 3

I had the same problem. I solved it with

pip install pathlib swagger_ui_bundle

Answer 4

It's caused by missing trailing slash. Just add slash at the end of your url and it will work.

Related issue https://github.com/zalando/connexion/issues/346 .