old_contents: class IsbnVerifier(object):
  
      def __init__(self, string):
          self.string = string
  
      def is_valid(self):
          return True
  
  
  
  def verify(isbn):
      return IsbnVerifier(isbn).is_valid()
  
new_contents: class IsbnVerifier(object):
  
      def __init__(self, string):
          self.string = string
  
      def is_valid(self):
          sum_so_far = 0
          for i, c in enumerate(IsbnVerifier.remove_slashes(self.string)):
              sum_so_far += IsbnVerifier.convert_char_to_int(c) * (10 - i)
          return sum_so_far % 11 == 0
  
      @staticmethod
      def remove_slashes(string):
          return "".join(filter(lambda char: char != "-", string))
  
      @staticmethod
      def convert_char_to_int(char):
          return int(IsbnVerifier.convert_x_to_ten(char))
  
      @staticmethod
      def convert_x_to_ten(char):
          return 10 if char == 'X' else char
  
  
  
  
  def verify(isbn):
      return IsbnVerifier(isbn).is_valid()
  
subject: Handle basic ISBN