> ## Documentation Index
> Fetch the complete documentation index at: https://python4ai.codewithsiva.dev/llms.txt
> Use this file to discover all available pages before exploring further.

# Environment variables

> Understanding environment config

## What are environment variables?

Environment variables are settings stored outside your code. Think of them as configuration that your program can read.

## The problem they solve

```python theme={null}
# BAD: Never hardcode sensitive data!
api_key = "sk-1234567890abcdef"  # Everyone can see this!
database = "production_database"  # Can't change without editing code
```

Problems:

* Secrets visible in code
* Can't share code safely
* Different settings for different computers

## How environment variables work

Environment variables live in your system, not your code:

```python theme={null}
import os

# Read from environment
api_key = os.environ.get('API_KEY')
database = os.environ.get('DATABASE_NAME', 'default.db')

print(f"Using database: {database}")
```

## Setting environment variables

You can set them temporarily in your terminal:

```bash theme={null}
# Mac/Linux
export API_KEY=sk-1234567890abcdef
python app.py

# Windows
set API_KEY=sk-1234567890abcdef
python app.py
```

But they disappear when you close the terminal!

## Reading in Python

```python theme={null}
import os

# Method 1: Get with default
api_key = os.environ.get('API_KEY', 'demo-key')

# Method 2: Check if exists
if 'API_KEY' in os.environ:
    api_key = os.environ['API_KEY']
else:
    print("No API key found")

# Method 3: Will crash if not found
api_key = os.environ['API_KEY']  # KeyError if missing!
```

## Common uses

* **API Keys**: `OPENAI_API_KEY`, `GITHUB_TOKEN`
* **Database URLs**: `DATABASE_URL`, `REDIS_URL`
* **App Settings**: `DEBUG=True`, `PORT=8000`
* **File Paths**: `LOG_DIR`, `UPLOAD_FOLDER`

## Important notes

* Environment variables are always strings
* Names are UPPERCASE by convention
* They're different on each computer
* They don't persist between terminal sessions

## What's next?

Setting variables manually is tedious. Let's use `.env` files for a better workflow.

<Card title="Using .env files" icon="file-shield" href="/tools/environment/dotenv">
  Easier way to manage variables
</Card>