Configuration & Environment Variables

⚙️ Configuration & Environment Variables

⚠️ The Problem: Hard-Coded Secrets

Many scripts hard-code sensitive information:

Copyimport mysql.connector

# ❌ NEVER DO THIS!
db = mysql.connector.connect(
    host="localhost",
    user="philip",
    password="MySecretPassword123",  # ← BAD!
    database="learning_blog"
)

The solution: Move secrets to a `.env` file that's never committed to Git.

📝 What is a .env File?

A Real .env File Example

Format Rules

• One setting per line: KEY=VALUE
• No quotes needed: DB_HOST=localhost (not "localhost")
• Comments with #: # This is a comment
• Empty lines ignored: Blank lines are skipped
• Case sensitive: DB_HOST and db_host are different
• No spaces around =: KEY=value (not KEY = value)

📦 Installing python-dotenv

To load `.env` files in Python, you need the python-dotenv package:

Copypip install python-dotenv

Add it to your requirements.txt:

Copymysql-connector-python==8.2.0
python-dotenv==1.0.0

🔓 Loading Environment Variables

The load_dotenv() Function

Copyfrom dotenv import load_dotenv
import os

# Load .env file from current directory (or parents)
load_dotenv()

# Now read variables using os.environ
host = os.environ['DB_HOST']
user = os.environ['DB_USER']
password = os.environ['DB_PASS']

print(f"Connecting to {host} as {user}")

With Explicit Path

If `.env` is in a specific location:

Copyfrom dotenv import load_dotenv
from pathlib import Path
import os

# Specify exact path to .env
env_path = Path("/var/www/.env")
load_dotenv(env_path)

host = os.environ['DB_HOST']

🔍 Accessing Variables

Method 1: Direct Access (Crashes if Missing)

Copyimport os

# This will crash if DB_HOST is not defined
host = os.environ['DB_HOST']
# KeyError: 'DB_HOST' if variable doesn't exist

Method 2: Safe Access with .get()

Copyimport os

# Returns the value, or None if not defined
host = os.environ.get('DB_HOST')

# With a default value if not defined
host = os.environ.get('DB_HOST', 'localhost')

# Check if it exists
if host is None:
    print("DB_HOST not defined!")

Copyhost = os.environ['DB_HOST']
# Crashes if missing
# Good for required settings

Copyhost = os.environ.get('DB_HOST', 'localhost')
# Returns default if missing
# Good for optional settings

🔄 Type Conversion

Converting to Different Types

Copyimport os
from dotenv import load_dotenv

load_dotenv()

# String (default, no conversion needed)
host = os.environ.get('DB_HOST')  # "localhost"

# Integer (port number)
port = int(os.environ.get('DB_PORT', '3306'))
# String "3306" → Integer 3306

# Boolean (debug mode)
debug = os.environ.get('DEBUG', 'false').lower() == 'true'
# String "true" → Boolean True

# Float (timeout in seconds)
timeout = float(os.environ.get('TIMEOUT', '30.5'))

print(f"Host: {host} (type: {type(host).__name__})")
print(f"Port: {port} (type: {type(port).__name__})")
print(f"Debug: {debug} (type: {type(debug).__name__})")

Helper Function for Booleans

Copydef get_bool_env(key: str, default: bool = False) -> bool:
    """Convert environment variable to boolean."""
    value = os.environ.get(key, str(default))
    return value.lower() in ('true', '1', 'yes', 'on')

# Usage:
debug = get_bool_env('DEBUG', False)

✅ Validating Configuration

Checking Required Variables

Copyfrom dotenv import load_dotenv
import os
import sys

load_dotenv()

# List of required variables
REQUIRED_VARS = ['DB_HOST', 'DB_USER', 'DB_PASS', 'DB_NAME']

# Check each one
missing = []
for var in REQUIRED_VARS:
    if var not in os.environ:
        missing.append(var)

if missing:
    print("❌ Missing required variables:")
    for var in missing:
        print(f"   - {var}")
    sys.exit(1)

print("✅ All required variables found!")

🔒 Security Best Practices

Never Commit .env to Git

Add `.env` to your `.gitignore` file:

File Permissions

On Linux/Mac, restrict `.env` to be readable only by the owner:

Copychmod 600 .env
# Now only the owner can read it

# Verify:
ls -la .env
# Should show: -rw------- (owner read/write only)

.env.example Template

Create a template showing what variables are needed (without real values):

🌍 Real-World Example: db_utils.py

Here's how the actual database utility script uses environment variables:

Copyfrom dotenv import load_dotenv
import os
import mysql.connector

# Load .env file
load_dotenv()

# Get database credentials from environment
DB_CONFIG = {
    'host': os.environ.get('DB_HOST'),
    'user': os.environ.get('DB_USER'),
    'password': os.environ.get('DB_PASS'),
    'database': os.environ.get('DB_NAME'),
    'port': int(os.environ.get('DB_PORT', '3306')),
    'charset': os.environ.get('DB_CHARSET', 'utf8mb4')
}

class DatabaseConnection:
    def __init__(self):
        self.connection = None

    def connect(self):
        try:
            self.connection = mysql.connector.connect(**DB_CONFIG)
            return True
        except Exception as e:
            print(f"❌ Connection failed: {e}")
            return False

⚠️ Common Mistakes

Copyimport os

host = os.environ['DB_HOST']
# KeyError: 'DB_HOST' not found!
# (You never called load_dotenv() to load the .env file)

Copyfrom dotenv import load_dotenv

load_dotenv()  # ← Add this!
host = os.environ['DB_HOST']

Copyport = os.environ['DB_PORT']  # This is a STRING "3306"

if port > 3000:  # ❌ TypeError: '>' not supported between str and int
    pass

Copyport = int(os.environ['DB_PORT'])  # ← Convert to integer

if port > 3000:  # ✅ Now it works
    pass

Copygit add .
git commit -m "Add configuration"
# Oops! You just committed DB_PASS with your real password!

Copy# Add to .gitignore BEFORE committing anything:
echo ".env" >> .gitignore
git add .gitignore
git commit -m "Add .gitignore"

💻 Coding Challenges

🎯 What's Next

Now that you can load configuration securely, the next chapter covers Database Connections — how to use this configuration to connect to MySQL/MariaDB and execute queries.