input: 
  def optimize_code(numbers):
      """ Optimize the given Python program which prints all elements of a list on new lines.
      >>> optimize_code([1, 2, 3, 4, 5, 6])
      '1\\n2\\n3\\n4\\n5\\n6'
      """
      return '\\n'.join(map(str, numbers))
  
output:     return '\\n'.join(map(str, numbers))