Environment variables are the standard way to configure apps.

Examples:

• SECRET_KEYSECRET_KEY
• DATABASE_URLDATABASE_URL
• MAIL_USERNAMEMAIL_USERNAME
• MAIL_PASSWORDMAIL_PASSWORD

Why env vars?

• keeps secrets out of code
• same container/code can run in dev/staging/prod

Local .env files

In local development, you can use a .env.env file.

Common library:

• python-dotenvpython-dotenv

Install:

pip install python-dotenv

pip install python-dotenv

Then Flask can load .env.env automatically when using flask runflask run (depending on setup), or you can load manually.

Do not commit .env

Add .env.env to .gitignore.gitignore.

Instead commit:

• .env.example.env.example

So people know what variables are required.

Accessing env vars in Python

import os
secret = os.environ.get("SECRET_KEY")

import os
secret = os.environ.get("SECRET_KEY")

Always define safe defaults for development, but never for production secrets.