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Multiple environments ​

It is convenient to load environment variables and use these to configure the app. This way, the app will be configured differently in different environments.

Setting manually ​

We can set environment variables manually in the terminal. They will be persisted only for the terminal session, so when you close the terminal they will be wiped.

bash
export X=123

echo $X
# 123
powershell
$env:X = 1

echo $env:X
# 123

This is useful, but if there are many variables it can be tedious.

Using env files ​

We can create separate .env files and choose which one to load based on the context.

bash
SECRET_KEY=21e29e988dec32f6eb6bd20bde3a14c1
DB_URL=sqlite:////home/user/project/dev.sqlite
bash
SECRET_KEY=4b02f45f952b5f050606efea58c35c2e
DB_URL=sqlite:///:memory:

WARNING

Add .env and .env.* to your .gitignore to prevent the environment files from being uploaded to version control.

Loading variables ​

We access environments variables using os.getenv("VAR_NAME").

We can import the environment variables into a config.py like this:

py
# config.py
import os
from dotenv import load_dotenv

MODE = os.getenv("MODE", "development")
load_dotenv(f".env.{MODE}")

PORT = int(os.getenv("PORT", 5000))
DEBUG = MODE in ["development", "testing"]
TESTING = MODE == "testing"
SECRET_KEY = os.getenv("SECRET_KEY")
SQLALCHEMY_DATABASE_URI = os.getenv("DB_URL")

These variables will change dynamically depending on what is available in the environment.

Switching modes ​

We can switch to testing before we test:

bash
export MODE="testing"
pytest
powershell
$env:MODE = "testing"
pytest

And switch back when developing:

bash
export MODE="development"
python -m src.run
powershell
$env:MODE = "development"
python -m src.run