docs: def main():
      """
      Main program entry point
      """
      args = command_line()
  
      # TODO: Decouple Book interface and implementation
      query = Book(
          title=args.title,
          author=args.author,
          max_results=args.max,
          language_code=args.language,
          fields=('title', 'authors', 'imageLinks', 'categories', 'description'),
      )
  
      if args.verbose:
          print('Request URL:')
          print(query.url)
          print(query.__dict__)
  
      # Temporary Display Interface
      books = query.json.get('items', None)
      if not books:
          raise AttributeError('Web Request Failed')
  
      for book in books:
          info = book['volumeInfo']
  
          # Retrieve ISBN/Reference Info
          if 'industryIdentifiers' in info:
              identifiers = dict([(ref['type'], ref['identifier']) for ref in info['industryIdentifiers']])
  
              # Prefer ISBN 13 over ISBN 10
              if 'ISBN_13' in identifiers:
                  isbn_id, isbn = 'ISBN_13', identifiers['ISBN_13']
              else:
                  isbn_id, isbn = identifiers.popitem()
  
          else:
              isbn_id, isbn = 'ISBN_##', 'N/A'
  
          # Format/Print
          display = 'Title: {title}\nAuthor: {authors}\n{isbn_id}: {isbn}\n'.format(
              title=info['title'],
              authors=', '.join(info.get('authors', ['N/A'])),
              isbn_id=isbn_id,
              isbn=isbn,
          )
  
          print(display)