How do I run flask on codebox IDE?
What exactly is happening when Run is clicked? 

It run the app.py on the codebox vm.
It maybe python app.py
To update, you fist should save your change(ctrl-s), and stop the run app, run it again.
When I create a Python box, I run command pip install -r requirements.txt then I click the Run button on the side and I can see the existing app run. 
What exactly is happening when Run is clicked?  
I've updated the existing file app.py, I made def hello(): return something new, however, it seems like codebox does not update and I still see hello world. 
What is happening when I click on the Run button? I'm trying to follow the Mega Flask Tutorial but haven't been able to make the flask server return the correct value, it always returns "hello world".