code: def set_percentage(x: Iterable[X], y: Iterable[X]) -> float:
      
      a, b = set(x), set(y)
  
      if not a:
          return 0.0
  
      return len(a & b) / len(a)
docs: What percentage of x is contained within y?
  
      :param set x: A set
      :param set y: Another set
      :return: The percentage of x contained within y