🔐 Python Tutorial — Environment Variables (.env)

Introduction 🌟

Environment Variables are secure values stored outside your code — such as API keys, database URLs, secrets, or configuration settings. Using a .env file helps you keep sensitive data out of your codebase.

Note

💡 Never hard-code secrets in Python files

💡 Use .env for development, environment variables for production

💡 Essential for APIs, automation, backend, cloud deployment

1. What Is a .env File? 🤔

A .env file contains key-value pairs like:

.env

API_KEY="abcdef12345"
DB_URL="postgresql://user:pass@localhost:5432/mydb"
DEBUG=True

✔ Do NOT commit this file to Git

2. Install python-dotenv 📦

install.sh

pip install python-dotenv

3. How to Load .env in Python 🧠

load_env.py

from dotenv import load_dotenv
import os

load_dotenv()  # reads .env file

print(os.getenv("API_KEY"))
print(os.getenv("DB_URL"))

✔ os.getenv() safely retrieves environment variables

4. Using dotenv in a Project Structure 📁

structure.txt

project/
│── app/
│   └── main.py
│── .env
│── requirements.txt

5. Setting Defaults if Value Missing 🎯

default.py

api_key = os.getenv("API_KEY", "default-key")

✔ Avoids crashes if variable missing

6. Environment Variables Without .env (Direct Shell) 🔧

Linux / macOS

bash_export.sh

export SECRET=12345
python main.py

Windows PowerShell

powershell_env.ps1

setx SECRET 12345

7. Protecting the .env File 🔐

.gitignore

# Ignore sensitive files
.env

✔ Prevents secrets from being pushed to GitHub

8. Type Conversion for Environment Variables 🔄

type_casting.py

DEBUG = os.getenv("DEBUG", "False").lower() == "true"
TIMEOUT = int(os.getenv("TIMEOUT", "30"))

9. Using Environment Variables in Config Modules ⚙️

config.py

from dotenv import load_dotenv
import os

load_dotenv()

class Config:
    API_KEY = os.getenv("API_KEY")
    DEBUG = os.getenv("DEBUG") == "True"
    DATABASE_URL = os.getenv("DB_URL")

✔ Centralizes configuration

10. Using Environment Variables in FastAPI / Flask 🚀

fastapi_example.py

from fastapi import FastAPI
import os
from dotenv import load_dotenv

load_dotenv()

app = FastAPI()

@app.get("/config")
def config():
    return {"debug": os.getenv("DEBUG")}

11. Nested or Multiple .env Files 📂

Useful for development vs production.

dotenv_multiple.py

load_dotenv(".env.development")
load_dotenv(".env.production")  # overrides

12. Accessing .env Inside Docker 🐳

docker_run.sh

docker run --env-file .env my_image

✔ Docker injects variables into container

13. Testing with Environment Variables 🧪

test_env.py

import os
import pytest

def test_env(monkeypatch):
    monkeypatch.setenv("MODE", "TEST")
    assert os.getenv("MODE") == "TEST"

14. Example: Secure Database Connection 🔗

db_connection.py

import os
from dotenv import load_dotenv
import psycopg2

load_dotenv()

conn = psycopg2.connect(os.getenv("DB_URL"))
print("Connected!")

15. Final Recommended .env Structure 📘

.env

# Application
DEBUG=True
SECRET_KEY="super-secret-key"

# Database
DB_HOST=localhost
DB_USER=user
DB_PASS=password
DB_NAME=app_db

# API keys
API_KEY_SERVICE1="key123"
API_KEY_SERVICE2="key456"

Best Practices 💡

  • ✔ Never commit .env to Git
  • ✔ Use `.env.example` without secrets for sharing
  • ✔ Override with real env vars in production (not .env)
  • ✔ Use tools like dotenv, pydantic for secure configs
  • ✔ Rotate sensitive keys regularly

Conclusion 🎉

>>“Environment Variables keep your secrets safe and your apps flexible — master them, and your applications become truly production-ready.” ✨

You now understand Environment Variables (.env) in Python! Want the next topic? Try Secrets Management, Deployment Strategies, Docker Compose Env, or Pydantic Settings. Just tell me! 😊