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GMAIL CLEANUP - CHALLENGE 3 SOLUTION
Chapter 2: Configuration Management
Challenge: Error Handling & Logging
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PROBLEM:
Enhance config loading with error handling:
1. Catch missing .env file gracefully
2. Handle type conversion errors
3. Print helpful error messages
4. Test with missing/invalid values

SOLUTION:
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File: config.py (final version with error handling)

import os
import re
import sys
from pathlib import Path
from dotenv import load_dotenv

class Config:
    """Application configuration with comprehensive error handling."""

    def __init__(self):
        self.valid = False
        self.errors = []

        # Try to load .env file
        env_file = Path(__file__).parent / ".env"
        if not env_file.exists():
            print(f"⚠️  .env not found at {env_file}")
            print("   Copy .env.example to .env and edit it")
            return

        try:
            load_dotenv(env_file)
        except Exception as e:
            self.errors.append(f"Failed to load .env: {e}")
            return

        # Load variables with error handling
        try:
            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'))
            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'))
        except ValueError as e:
            self.errors.append(f"Configuration value is not a number: {e}")
            return
        except Exception as e:
            self.errors.append(f"Unexpected error loading config: {e}")
            return

        self.valid = True

    def validate(self) -> bool:
        """Validate configuration after loading."""

        if self.errors:
            for error in self.errors:
                print(f"❌ {error}")
            return False

        # Email validation
        if not self.gmail_user:
            print("❌ GMAIL_USER is empty")
            return False

        email_pattern = r'^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$'
        if not re.match(email_pattern, self.gmail_user):
            print(f"❌ GMAIL_USER '{self.gmail_user}' is invalid")
            return False

        # Numeric validation
        if self.api_timeout <= 0:
            print("❌ API_REQUEST_TIMEOUT must be positive")
            return False

        if self.max_results <= 0:
            print("❌ MAX_RESULTS must be positive")
            return False

        print("✅ Configuration is valid!")
        return True


def main():
    """Test configuration loading."""
    print("=" * 60)
    print("CONFIGURATION LOADER TEST")
    print("=" * 60)

    config = Config()

    if not config.valid:
        print("\n❌ Failed to load configuration")
        return False

    if not config.validate():
        print("\n❌ Configuration validation failed")
        return False

    print(f"\nConfiguration loaded:")
    print(f"  Gmail User: {config.gmail_user}")
    print(f"  API Timeout: {config.api_timeout}s")
    print(f"  Max Results: {config.max_results}")
    print(f"  Delete emails older than: {config.days_old} days")

    return True


if __name__ == "__main__":
    success = main()
    sys.exit(0 if success else 1)


ERROR HANDLING SCENARIOS
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1. MISSING .ENV FILE
Error:
⚠️  .env not found at /path/to/.env
   Copy .env.example to .env and edit it

2. INVALID EMAIL
Error:
❌ GMAIL_USER 'notanemail' is invalid

3. TYPE CONVERSION ERROR
Error:
❌ Configuration value is not a number: invalid literal for int()

4. EMPTY VALUE
Error:
❌ GMAIL_USER is empty


TESTING ALL SCENARIOS
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# Scenario 1: Valid config
python config.py
Expected: ✅ Configuration is valid!

# Scenario 2: Missing .env
rm .env
python config.py
Expected: ⚠️  .env not found

# Scenario 3: Invalid email in .env
GMAIL_USER=notanemail
python config.py
Expected: ❌ GMAIL_USER 'notanemail' is invalid

# Scenario 4: Non-numeric timeout
API_REQUEST_TIMEOUT=abc
python config.py
Expected: ❌ Configuration value is not a number


KEY PATTERNS
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✅ Try/except for file I/O
✅ Try/except for type conversion
✅ Graceful error messages
✅ Early return on failure
✅ Helpful hints for fixing

This is production-ready error handling!

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