Being deployment specific with instance folders

By default, the instance folder is picked up from the application automatically if we have a folder named instance in our application at the application level:

my_app/
    - app.py
    - instance/
        - config.cfg

We can also explicitly define the absolute path of the instance folder using the instance_path parameter on our application object:

app = Flask(
    __name__, instance_path='/absolute/path/to/instance/folder'
)

To load the configuration file from the instance folder, we will use the instance_relative_config parameter on the application object:

app = Flask(__name__, instance_relative_config=True)

This tells the application to load the configuration file from the instance folder. The following example shows how this will work:

app = Flask(
    __name__, instance_path='path/to/instance/folder',
    instance_relative_config=True
)
app.config.from_pyfile('config.cfg', silent=True)

In the preceding code, first, the instance folder is loaded from the given path, and then, the configuration file is loaded from the file named config.cfg in the given instance folder. Here, silent=True is optional and used to suppress the error in case config.cfg is not found in the instance folder. If silent=True is not given and the file is not found, then the application will fail, giving the following error:

IOError: [Errno 2] Unable to load configuration file (No such file or directory): '/absolute/path/to/config/file'