http://127.0.0.1:5000/swagger-ui/

app.py

from flask import Flask
from flask_apispec import use_kwargs, marshal_with

from marshmallow import fields, Schema

from flask import make_response
from flask_apispec.views import MethodResource

from apispec import APISpec
from apispec.ext.marshmallow import MarshmallowPlugin
from flask_apispec.extension import FlaskApiSpec


app = Flask(__name__)

class PetSchema(Schema):
	pet_id = fields.Str(required=False)
	name = fields.Str(required=False)
	category = fields.Str(required=False)
	size = fields.Str(required=False)


pet = {"pet_id": 100, "name": "pet1", "category":"category1", "size" :"size1"}
pets = [ { "pet_id": 100, "name": "pet1", "category":"category1", "size" :"size1"},
		{"pet_id": 200, "name": "pet2", "category":"category2", "size" :"size2"}]


@app.route('/pets')
@marshal_with(PetSchema(many=True))
def get_pets(**kwargs):
    return pets


class PetResource(MethodResource):

    @use_kwargs({"pet_id": fields.Str(required=True)}, locations=["query"])
    @marshal_with(PetSchema)
    def get(self, pet_id):
        return pet

    @use_kwargs(PetSchema)
    @marshal_with(PetSchema, code=201)
    def post(self, **kwargs):
        return pet

    @use_kwargs({"pet_id": fields.Str(required=True)}, locations=["query"])
    @marshal_with(PetSchema)
    def put(self, pet_id, **kwargs):
        return pet

    @use_kwargs({"pet_id": fields.Str(required=True)}, locations=["query"])
    @marshal_with(None, code=204)
    def delete(self, pet_id):
        return make_response('', 204)



app.config.update({
    'APISPEC_SPEC': APISpec(
        title='pets',
        version='v1',
        plugins=[MarshmallowPlugin()],
    ),
    'APISPEC_SWAGGER_URL': '/swagger/',
})


docs = FlaskApiSpec(app)

docs.register(get_pets)

app.add_url_rule('/pet', view_func=PetResource.as_view(PetResource.__name__.lower()) )
        # with app.app_context():
docs.register(PetResource)

if __name__ == "__main__":
	app.run()