Running a Script with Environment Variables

What Are Environment Variables?

environment variables are dynamic values
used to store configuration settings

API keys and secrets	sensitive data needed to interact with external services
database connection strings	information required to connect to databases
configuration settings	various settings
environment-specific values	values that differ between development, testing, and production environments

Why Use Environment Variables?

Security	store sensitive information in environment variables keeps them out of the source code reduces the risk of exposing sensitive data when sharing or committing code
Flexibility	environment variables allow easy switching between configurations no need to modify code useful when deploying the application across multiple environments (e.g., development, staging, and production)
Configuration Management	use environment variables to centralize configuration management manage settings externally makes it easier to update and maintain configurations
Consistency	environment variables provide a consistent way to manage settings across different platforms and deployment environments ensures application behaves as expected regardless of where it is run

Setting Environment Variables

set environment variables in the shell before running script
in Unix-based system

export DATABASE_URL="postgres://user:password@localhost/dbname"
export SECRET_KEY="supersecretkey"
export API_KEY="your_api_key"

in Windows

set DATABASE_URL="postgres://user:password@localhost/dbname"
set SECRET_KEY="supersecretkey"
set API_KEY="your_api_key"

when the script runs it has access to the environment variables

Example Python Script

import os

def main() -> None:
    database_url = os.getenv('DATABASE_URL')
    secret_key = os.getenv('SECRET_KEY')
    api_key = os.getenv('API_KEY')

    if not all([database_url, secret_key, api_key]):
        raise ValueError("Missing one or more environment variables: DATABASE_URL, SECRET_KEY, API_KEY")

    print(f"Connecting to database at {database_url}")
    print(f"Using secret key: {secret_key}")
    print(f"API key: {api_key}")
    # Add application logic here

if __name__ == "__main__":
    main()

Using a .env File with python-dotenv

use use a .env file with python-dotenv to manage environment variables
stores environment variables in a file and load them into the app
create a .env file in project's root of directory

DATABASE_URL=postgres://user:password@localhost/dbname
SECRET_KEY=supersecretkey
API_KEY=your_api_key

load environment variables in main.py
modify script to use python-dotenv to load the environment variables from the .env file

import os
from dotenv import load_dotenv

def main():
    # Load environment variables from .env file
    load_dotenv()

    database_url = os.getenv('DATABASE_URL')
    secret_key = os.getenv('SECRET_KEY')
    api_key = os.getenv('API_KEY')

    if not all([database_url, secret_key, api_key]):
        raise ValueError("Missing one or more environment variables: DATABASE_URL, SECRET_KEY, API_KEY")

    print(f"Connecting to database at {database_url}")
    print(f"Using secret key: {secret_key}")
    print(f"API key: {api_key}")
    # Add your application logic here

if __name__ == "__main__":
    main()

Best Practices

do not write secrets in the code	it will end up being as public in the code can result in leaks
Do not commit the .env file to version control	add .env to your .gitignore file ensure file is not included in version control system
duse separate .env files for different environments	use separate .env files for different environments for example : .env.development, .env.testing, and .env.production load the appropriate file based on the environment