def findMinAndMax(L):

    if L == []:

        return None,None

    else:

        min=L[0]

        max=L[0]

        for s in L:

            if  max<=s:  # 如果最大值比s小，最大值为s

                max = s

            elif min>=s:  # 如果最小值比s大，最大值为s

                min = s

        return min,max

print(findMinAndMax([1,2,3,4,5,6]))

# 测试

if findMinAndMax([]) != (None, None):

    print('测试失败!')

elif findMinAndMax([7]) != (7, 7):

    print('测试失败!')

elif findMinAndMax([7, 1]) != (1, 7):

    print('测试失败!')

elif findMinAndMax([7, 1, 3, 9, 5]) != (1, 9):

    print('测试失败!')

else:

    print('测试成功!')

结果为：

(1, 6)

测试成功!