input: Write a function to generate an HTML table displaying information about the top 10 bestselling books in a specific genre from a SQLite database. The function should take a genre as input and return the HTML code for the table. If the genre is not provided, use 'Fantasy' as the default genre.
  
  def generate_html_table(genre='Fantasy'):
      # connect to the database
      conn = sqlite3.connect('books.db')
      c = conn.cursor()
  
      # retrieve the data
      c.execute('''SELECT title, author, genre, sales
                   FROM Books
                   WHERE genre=?
                   ORDER BY sales DESC
                   LIMIT 10''', (genre,))
  
      # save the results
      results = c.fetchall()
  
      # generate the HTML code
      html = '<table>'
      html += '<tr><th>Title</th><th>Author</th><th>Genre</th><th>Sales</th></tr>'
  
      for result in results:
          title = result[0]
          author = result[1]
          genre = result[2]
          sales = result[3]
  
          html += f'<tr><td>{title}</td><td>{author}</td><td>{genre}</td><td>{sales}</td></tr>'
  
      html += '</table>'
  
      return html
  
  assert generate_html_table('Romance') != ''
  assert generate_html_table('Mystery') != ''
  assert generate_html_table('Science Fiction') != ''
  assert generate_html_table() != ''
  assert generate_html_table('') != ''
output: 
  def generate_html_table(genre='Fantasy'):
      conn = sqlite3.connect('books.db')
      c = conn.cursor()
      c.execute('''SELECT title, author, genre, sales
                   FROM Books
                   WHERE genre=?
                   ORDER BY sales DESC
                   LIMIT 10''', (genre,))
      results = c.fetchall()
      html = '<table>'
      html += '<tr><th>Title</th><th>Author</th><th>Genre</th><th>Sales</th></tr>'
      for result in results:
          title = result[0]
          author = result[1]
          genre = result[2]
          sales = result[3]
          html += f'<tr><td>{title}</td><td>{author}</td><td>{genre}</td><td>{sales}</td></tr>'
      html += '</table>'
      return html
  