Configuration Management

Gmail Cleanup — Practical Scripting
Course 1 · Chapter 2 · Configuration Management

🔧 Configuration Management

Configuration should never be hardcoded! This chapter teaches you how to load settings from environment variables using .env files, validate them, and handle errors gracefully. This is a critical skill for secure, portable applications.

📋 Why Configuration Management Matters

Consider this dangerous code:

# ❌ BAD: Hardcoded credentials!
GMAIL_USER = "my-email@gmail.com"
API_TIMEOUT = 10

Problems:

  • Email is visible in the code
  • Can't change settings without editing the code
  • Different values needed for development vs. production
  • Easy to accidentally commit secrets to Git

The solution: .env files + load_dotenv()

🔐 The .env Pattern

Create a config.py module:

import os
from pathlib import Path
from dotenv import load_dotenv

# Load .env file from same directory as this script
ENV_FILE = Path(__file__).parent / ".env"
load_dotenv(ENV_FILE)

class Config:
    """Application configuration."""

    def __init__(self):
        # Gmail settings
        self.gmail_user = os.environ.get('GMAIL_USER')
        self.api_timeout = int(os.environ.get('API_REQUEST_TIMEOUT', '10'))
        self.max_results = int(os.environ.get('MAX_RESULTS', '100'))

        # Cleanup settings
        self.days_old = int(os.environ.get('DELETE_OLDER_THAN_DAYS', '365'))
        self.min_attachment_mb = int(os.environ.get('MIN_ATTACHMENT_SIZE_MB', '10'))

    def validate(self) -> bool:
        """Validate required configuration."""
        if not self.gmail_user:
            print("❌ Missing GMAIL_USER in .env")
            return False

        if '@' not in self.gmail_user:
            print("❌ GMAIL_USER must be a valid email")
            return False

        return True

📝 Using Configuration in Your Script

from config import Config

def main():
    # Load configuration
    config = Config()

    # Validate it
    if not config.validate():
        return False

    # Use it
    print(f"Cleaning emails from: {config.gmail_user}")
    print(f"Deleting emails older than: {config.days_old} days")

    return True

if __name__ == "__main__":
    main()

⚠️ Common Configuration Errors

Error 1: .env file not found

Cause: File is in wrong directory or has wrong name

Fix: Make sure .env is in the same folder as config.py

Error 2: Variables are None

Cause: Variable name in code doesn't match .env

Fix: Case matters! Use exact same names

Error 3: Type conversion errors

Cause: Trying to convert non-numeric value to int

Fix: Validate that .env values are correct type

💻 Coding Challenges

Challenge 1: Create config.py

Build a Config class that:

  1. Loads .env file from current directory
  2. Reads GMAIL_USER, API_REQUEST_TIMEOUT, MAX_RESULTS
  3. Uses defaults for timeout (10) and max_results (100)
  4. Returns all values

Goal: Create reusable configuration module.

→ Solution

Challenge 2: Configuration Validation

Extend Config.validate() to check:

  1. GMAIL_USER is not empty
  2. GMAIL_USER contains @ symbol (valid email)
  3. API_REQUEST_TIMEOUT is positive number
  4. Return True if all valid, False otherwise

Goal: Practice data validation.

→ Solution

Challenge 3: Error Handling & Logging

Enhance config loading with error handling:

  1. Catch missing .env file gracefully
  2. Handle type conversion errors
  3. Print helpful error messages (what's wrong, how to fix)
  4. Test with missing/invalid values

Goal: Build robust configuration system.

→ Solution