Environment Variables

Environment variables are used to store configuration settings and other information that applications need to function. They provide a way to separate code from configuration, making applications more flexible and secure.

Key Concepts

Environment Variable:
- A variable that is set outside the application, typically in the operating system or a configuration file.
- Example: API_KEY=12345abcde
Sensitive Information:
- Environment variables are often used to store sensitive information such as API keys, tokens, and database credentials to keep them out of the source code.
- Example: DB_PASSWORD=mysecretpassword

Using Environment Variables in Python

Python provides several ways to access environment variables, with the os module being the most common.

Setting Environment Variables

Setting in the Operating System:
```
    export API_KEY=12345abcde
```
Setting in a .env File: Create a .env file in your project directory:
```
    API_KEY=12345abcde
```

Accessing Environment Variables

Using os Module:

    import os

    api_key = os.getenv('API_KEY')
    print(api_key)

Using `python-dotenv` to Load `.env` Files

Install python-dotenv:
```
    pip install python-dotenv
```

Load Environment Variables from .env File:

    from dotenv import load_dotenv
    import os

    load_dotenv()  # Load environment variables from .env file

    api_key = os.getenv('API_KEY')
    print(api_key)

Hiding Sensitive Variables

Keep .env File Out of Version Control: Add .env to your .gitignore file to prevent it from being committed to version control.
```
    # .gitignore
    .env
```

Example: Using Environment Variables in a Python Application

Create .env File:

    API_KEY=12345abcde
    DB_PASSWORD=mysecretpassword

Load and Use Environment Variables:

    from dotenv import load_dotenv
    import os

    load_dotenv()  # Load environment variables from .env file

    api_key = os.getenv('API_KEY')
    db_password = os.getenv('DB_PASSWORD')

    print(f'API Key: {api_key}')
    print(f'Database Password: {db_password}')

Common Use Cases

Accessing API Keys:

    import os
    import requests
    from dotenv import load_dotenv

    load_dotenv()  # Load environment variables

    api_key = os.getenv('API_KEY')
    url = f'https://api.example.com/data?api_key={api_key}'

    response = requests.get(url)
    print(response.json())

Connecting to a Database:

    import os
    import psycopg2
    from dotenv import load_dotenv

    load_dotenv()  # Load environment variables

    db_password = os.getenv('DB_PASSWORD')

    connection = psycopg2.connect(
        database="mydatabase",
        user="myuser",
        password=db_password,
        host="localhost",
        port="5432"
    )

    cursor = connection.cursor()
    cursor.execute("SELECT version();")
    record = cursor.fetchone()
    print(f"You are connected to - {record}\n")

    cursor.close()
    connection.close()

Notes about Python