old_contents: def sum_of_multiples(limit, factors):
      return sum(filter(lambda n: n < limit,
                        {f*i for i in range(1, limit) for f in factors}))
  
new_contents: def sum_of_multiples(limit, factors):
      return sum({n for f in factors for n in range(f, limit, f)})
  
subject: Use more optimal method of getting multiples