If your application takes its configuration from environment variables, like a 12-factor application, launching it in development is not very practical because you have to set those environment variables yourself.

pip install python-dotenv

To help you with that, you can add Python-dotenv to your application to make it load the configuration from a .env file when it is present (e.g. in development) while remaining configurable via the environment:

from dotenv import load_dotenv

load_dotenv()  # take environment variables from .env.

Code of your application, which uses environment variables (e.g. from os.environ or
os.getenv) as if they came from the actual environment.
By default, load_dotenv doesn't override existing environment variables.

To configure the development environment, add a .env in the root directory of your project:

.
├── .env
└── foo.py

The syntax of .env files supported by python-dotenv is similar to that of Bash:

# Development settings
DOMAIN=example.org
ADMIN_EMAIL=admin@${DOMAIN}
ROOT_URL=${DOMAIN}/app

If you use variables in values, ensure they are surrounded with { and }, like ${DOMAIN}, as bare variables such as $DOMAIN are not expanded.

You will probably want to add .env to your .gitignore, especially if it contains secrets like a password.