old_contents: f1, f2, s, n = 0, 1, 0, 4000000
  while f2 < n:
      f2, f1 = f1, f1 + f2
      if f2 % 2 == 0:
          s += f2
  print s
  
new_contents: def sum_even_fibonacci_numbers_1():
      f1, f2, s, = 0, 1, 0,
      while f2 < 4000000:
          f2, f1 = f1, f1 + f2
          if f2 % 2 == 0:
              s += f2
      return s
  def sum_even_fibonacci_numbers_2():
      s, a, b = 0, 1, 1
      c = a + b
      while c < 4000000:
          s += c
          a = b + c
          b = a + c
          c = a + b
      return s
  
subject: Add a second Python implementation of problem 2