Flask App Configuration

March 12, 2025

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The dotenv package can be used to load configuration settings for a Flask app. The configuration is defined in a .env file which is ignored by version control to ensure items like API keys and passwords are not shared with others.

In the example project shown below, the __init__.py is the application factory for the Flask app. It loads the configuration settings from the .env file which are stored in the app.config attribute. It also registers the routes which are discussed next.

.
├── .env
├── pyproject.toml
├── src/
│   └── flaskr/
│       ├── __init__.py
│       └── routes.py
└── uv.lock

# __init__.py

from flask import Flask
from dotenv import dotenv_values
from . import routes

def create_app():
    app = Flask(__name__)

    # Load configuration from .env file then store configuration settings in the
    # config attribute of the flask object
    config = dotenv_values(".env")
    app.config.from_mapping(config)

    app.register_blueprint(routes.bp)

    return app

Contents of the .env file are shown below.

USERNAME="homer"
PASSWORD="alpha12345"

The routes.py file (see below) loads the USERNAME and PASSWORD from the current_app.config attribute. Note that the USERNAME and PASSWORD are defined in the .env file. This approach allows all the configuration settings for the Flask app to be defined in the .env file.

# routes.py

from flask import Blueprint
from flask import current_app

bp = Blueprint("routes", __name__)

@bp.route("/")
def home():
    """Home page."""
    return "<p>Hello there!</p>"

@bp.route("/config")
def read_config():
    """Display config values."""
    config = current_app.config
    username = config["USERNAME"]
    password = config["PASSWORD"]
    return f"<p>USERNAME is {username}</p><p>PASSWORD is {password}</p>"

See the pythonic/projects/flask-config directory in the pythonic repository on GitHub for the example code. The .env file is not in the repository because it is ignored by git; therefore, it must be created with the contents shown above to run the example code.