Unable to load configuration file from instance folder when deploying app

Question

I set up a new virtualenv for my app, to clean up the installed packages. I have a config.py file in the app's instance folder. There are two configs, one for dev in the 'instance' folder and one for production in the root folder. The app worked in the old env, but now I get an error that it couldn't find the config file. Why am I getting this error and how do I fix it?

Traceback (most recent call last):
  File "application.py", line 12, in <module>
    application.config.from_pyfile('config.py')
  File "/Users/pavsidhu/Envs/test/lib/python2.7/site-packages/flask/config.py", line 128, in from_pyfile
    with open(filename) as config_file:
IOError: [Errno 2] Unable to load configuration file (No such file or directory): '/Users/pavsidhu/Envs/test/var/application-instance/config.py'

My project structure looks like:

/Users/pavsidhu/Envs/test/
    lib/python-3.4/site-packages/
    bin/
    application.py
    static/
    templates/
    instance/
        config.py

Answer 1

Flask thinks your app is installed in the env because you put it in the same base directory as the env. This behavior is described in detail in the docs.

Installed module or package:

$PREFIX/lib/python2.X/site-packages/myapp
$PREFIX/var/myapp-instance

$PREFIX is the prefix of your Python installation.

Flask expects the instance folder to be at var/myapp-instance when installed this way. (The structure isn't exactly the same, but it's similar enough to fool Flask's detection function.)

You should not mix your project structure with the virtualenv structure. Separate the two:

my_env/
    lib/
    bin/
my_project/
    my_app/
        __init__.py
        static/
        templates/
    instance/

See the comment discussion moved to chat for further details.