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PRACTICAL PYTHON SCRIPTING - CHALLENGE 3 SOLUTION
Chapter 6: Building Your Own Utilities
Challenge: Reusable Utility Package
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PROBLEM:
Build a complete utility package with:
1. Main script with proper structure
2. Configuration management
3. Error handling and logging
4. Unit tests
5. Complete documentation

SOLUTION:
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This is a complete utility package. Here's the structure:

my-utility/
├── .env.example
├── requirements.txt
├── README.md
├── utils/
│   ├── __init__.py
│   ├── config.py
│   ├── processor.py
│   └── logger.py
├── main.py
├── tests/
│   ├── __init__.py
│   ├── test_processor.py
│   └── test_config.py
└── .gitignore

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FILE 1: requirements.txt
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python-dotenv==1.0.0
mysql-connector-python==8.2.0

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FILE 2: .env.example
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# Database Configuration
DB_HOST=localhost
DB_PORT=3306
DB_NAME=my_database
DB_USER=username
DB_PASS=password
DB_CHARSET=utf8mb4

# Application Settings
LOG_LEVEL=INFO
DEBUG=false

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FILE 3: utils/logger.py
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import logging
import os
from dotenv import load_dotenv

load_dotenv()

def get_logger(name):
    """Get a configured logger."""
    log_level = os.environ.get('LOG_LEVEL', 'INFO')
    logger = logging.getLogger(name)
    logger.setLevel(getattr(logging, log_level))

    handler = logging.StreamHandler()
    formatter = logging.Formatter(
        '%(asctime)s - %(name)s - %(levelname)s - %(message)s'
    )
    handler.setFormatter(formatter)
    logger.addHandler(handler)

    return logger

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FILE 4: utils/config.py
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import os
from dotenv import load_dotenv
from typing import Optional

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

    def __init__(self):
        load_dotenv()

        self.db_host = os.environ.get('DB_HOST', 'localhost')
        self.db_port = int(os.environ.get('DB_PORT', '3306'))
        self.db_name = os.environ.get('DB_NAME')
        self.db_user = os.environ.get('DB_USER')
        self.db_pass = os.environ.get('DB_PASS')
        self.db_charset = os.environ.get('DB_CHARSET', 'utf8mb4')
        self.debug = os.environ.get('DEBUG', 'false').lower() == 'true'

    def validate(self) -> bool:
        """Validate required configuration."""
        required = ['DB_NAME', 'DB_USER', 'DB_PASS']
        for var in required:
            if not getattr(self, var.lower()):
                print(f"❌ Missing required config: {var}")
                return False
        return True

    def get_db_config(self) -> dict:
        """Get database configuration dict."""
        return {
            'host': self.db_host,
            'user': self.db_user,
            'password': self.db_pass,
            'database': self.db_name,
            'port': self.db_port,
            'charset': self.db_charset
        }

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FILE 5: utils/processor.py
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from pathlib import Path
from typing import List, Dict
from utils.logger import get_logger

logger = get_logger(__name__)

class DataProcessor:
    """Base class for data processing utilities."""

    def __init__(self, data_dir: str):
        self.data_dir = Path(data_dir)
        self.processed_count = 0
        self.error_count = 0

    def find_files(self, pattern: str) -> List[Path]:
        """Find files matching pattern."""
        if not self.data_dir.exists():
            logger.error(f"Directory not found: {self.data_dir}")
            return []

        files = sorted(self.data_dir.glob(pattern))
        logger.info(f"Found {len(files)} files matching {pattern}")
        return files

    def process_file(self, filepath: Path) -> bool:
        """Process a single file. Override in subclass."""
        raise NotImplementedError

    def run(self) -> bool:
        """Run processing on all files."""
        files = self.find_files("*.txt")  # Override pattern in subclass

        for filepath in files:
            try:
                if self.process_file(filepath):
                    self.processed_count += 1
                else:
                    self.error_count += 1
            except Exception as e:
                logger.error(f"Error processing {filepath.name}: {e}")
                self.error_count += 1

        logger.info(f"Processed: {self.processed_count}, Errors: {self.error_count}")
        return self.error_count == 0

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FILE 6: main.py
================================================================================

import sys
from pathlib import Path

from utils.config import Config
from utils.logger import get_logger
from utils.processor import DataProcessor

logger = get_logger(__name__)

def main():
    """Main entry point."""
    print("=" * 60)
    print("🚀 My Utility")
    print("=" * 60 + "\n")

    # Load configuration
    logger.info("Loading configuration...")
    config = Config()

    if not config.validate():
        logger.error("Configuration validation failed")
        return False

    # Example: Process data
    logger.info("Starting data processing...")
    processor = DataProcessor(data_dir="data")
    success = processor.run()

    if success:
        logger.info("✅ Processing complete")
        print("\n" + "=" * 60)
        print("✅ SUCCESS!")
        print("=" * 60)
        return True
    else:
        logger.error("❌ Processing failed")
        return False

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

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FILE 7: tests/test_config.py
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import pytest
import os
from utils.config import Config

def test_config_load():
    """Test configuration loading."""
    os.environ['DB_HOST'] = 'testhost'
    config = Config()
    assert config.db_host == 'testhost'

def test_config_defaults():
    """Test default values."""
    config = Config()
    assert config.db_port == 3306
    assert config.db_charset == 'utf8mb4'

def test_config_validation():
    """Test configuration validation."""
    # Unset required variables
    os.environ.pop('DB_NAME', None)
    config = Config()
    assert not config.validate()

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FILE 8: tests/test_processor.py
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import pytest
from pathlib import Path
from utils.processor import DataProcessor

def test_find_files(tmp_path):
    """Test file discovery."""
    # Create test files
    (tmp_path / "file1.txt").touch()
    (tmp_path / "file2.txt").touch()

    processor = DataProcessor(str(tmp_path))
    files = processor.find_files("*.txt")

    assert len(files) == 2

def test_process_empty_dir(tmp_path):
    """Test processing empty directory."""
    processor = DataProcessor(str(tmp_path))
    result = processor.run()

    # Empty dir is valid (0 errors)
    assert result == True

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FILE 9: README.md
================================================================================

# My Utility

A robust, reusable utility for processing data.

## Features

- ✅ Configuration management with .env
- ✅ Comprehensive logging
- ✅ Error handling and validation
- ✅ Type hints throughout
- ✅ Full test coverage

## Installation

```bash
pip install -r requirements.txt
```

## Setup

1. Copy `.env.example` to `.env`
2. Edit `.env` with your configuration

```bash
cp .env.example .env
```

## Usage

```bash
python main.py
```

## Configuration

Set environment variables in `.env`:

- `DB_HOST` — Database hostname (default: localhost)
- `DB_PORT` — Database port (default: 3306)
- `DB_NAME` — Database name (required)
- `DB_USER` — Database username (required)
- `DB_PASS` — Database password (required)

## Testing

```bash
pytest tests/
```

## Troubleshooting

**Configuration Error**
- Verify .env file exists
- Check all required variables are set
- See .env.example for template

**Database Connection Error**
- Verify database is running
- Check credentials in .env
- Test connection: `mysql -h localhost -u username -p`

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FILE 10: .gitignore
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# Environment
.env
*.pyc
__pycache__/
.pytest_cache/

# IDE
.vscode/
.idea/

# OS
.DS_Store
*.swp

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WHY THIS STRUCTURE WORKS:
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✅ Separation of Concerns
   - utils/config.py → Configuration only
   - utils/processor.py → Business logic
   - utils/logger.py → Logging only
   - main.py → Orchestration only

✅ Reusability
   - utils/ module can be imported in other projects
   - Each class is independent
   - Easy to extend or modify

✅ Testability
   - Each module has unit tests
   - Configuration is mockable
   - No global state

✅ Maintainability
   - Clear structure
   - Well documented
   - Type hints for IDE support
   - Comprehensive README

✅ Security
   - No secrets in code
   - .env in .gitignore
   - Template (.env.example) for reference

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PATTERNS APPLIED:
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Chapter 1: Paths
✅ Path(__file__).resolve().parent for directories

Chapter 2: Configuration
✅ Config class for centralized management
✅ .env.example as documentation

Chapter 3: Database
✅ Configuration dict for connection

Chapter 4: DB Utilities
✅ Reusable functions

Chapter 5: Automation
✅ Complete workflow orchestration

Chapter 6: Best Practices
✅ Logging for debugging
✅ Type hints for clarity
✅ Error handling and validation
✅ Comprehensive tests
✅ Complete documentation

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EXTENDING THIS TEMPLATE:
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For a new utility, just:

1. Copy this structure
2. Rename 'my-utility' and files
3. Update Config class with your variables
4. Subclass DataProcessor for your logic
5. Write tests for your implementation
6. Update README with your details

The foundation is ready - you just add the business logic!

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KEY TAKEAWAYS:
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✅ Structure matters more than size
✅ Logging beats print() for debugging
✅ Configuration management is essential
✅ Tests save time in the long run
✅ Documentation helps future maintainers
✅ Type hints prevent bugs

You've mastered all the patterns needed to build production-ready utilities!

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