Environment variable management in Flask

Introduction

Environment variables help keep sensitive information like passwords safe and let you change settings without changing your code.

You want to keep your database password secret and not write it in your code.

You need to switch between development and production settings easily.

You want to share your code without sharing private keys or secrets.

You want to configure your app differently on your computer and on a server.

Syntax

Flask

import os

# Get an environment variable
value = os.getenv('VARIABLE_NAME', 'default_value')

Use os.getenv to read environment variables safely.

You can provide a default value if the variable is not set.

Examples

This reads the SECRET_KEY environment variable.

Flask

import os

secret_key = os.getenv('SECRET_KEY')

This reads the PORT variable or uses '5000' if not set.

Flask

import os

port = os.getenv('PORT', '5000')

This reads DEBUG and converts it to a boolean.

Flask

import os

debug_mode = os.getenv('DEBUG', 'False') == 'True'

Sample Program

This Flask app reads the SECRET_KEY and PORT from environment variables. It shows the secret key on the home page and runs on the specified port or 5000 by default.

Flask

import os
from flask import Flask

app = Flask(__name__)

# Set secret key from environment variable
app.config['SECRET_KEY'] = os.getenv('SECRET_KEY', 'defaultsecret')

@app.route('/')
def home():
    return f"Secret key is: {app.config['SECRET_KEY']}"

if __name__ == '__main__':
    port = int(os.getenv('PORT', '5000'))
    app.run(debug=True, port=port)

Important Notes

Never commit real secrets to your code repository.

Use a .env file with tools like python-dotenv during development to load environment variables.

Environment variables are strings; convert them if you need other types.

Summary

Environment variables keep sensitive info safe and separate from code.

Use os.getenv to read them with optional defaults.

Set different values for development and production easily.