如果你试图找到最大的数字，为什么你不断地追加到highest_score或lowest_score？难道你不想只附加最大值或最小值吗？为什么不先计算一下呢？

nums = [6, 8, 9, 5, 3, 3, 5, 3]
highest_score = []
lowest_score = []

def calculate_Scores(nums):
  i = 1
  max = min = nums[0]
  # first, calculate the max and min.
  while i < len(nums):  # (possible improvement: replace this with a for loop)
    if nums[i] > max:
      max = nums[i]    # replace max with the new max
    if nums[i] < min:
      min = nums[i]    # replace min with the new min
    i += 1
  # now that you've done that, add them to the highest_score and lowest_score
  highest_score.append(max)
  lowest_score.append(min)

请注意，虽然这可能是一个有用的教育练习，但在这种情况下（或者在任何其他情况下，您试图找到一个以某种方式胜过其他元素的元素），没有实际的理由不使用内置函数max()和min()。

There is a more easy way to do it 
If you want to user For Loop => 

nums = [6, 8, 9, 5, 3, 3, 5, 3]
highest_number = 0

for n in nums:
    if n > highest_score:
        highest_score = n
print(highest_number)

Or there is a built in function called max()which will do the same .

For ext print(max(nums)) => 9