Python 使用迭代查找一个list中最小和最大值，并返回一个tuple

def findMinAndMax(L):
    if len(L) == 0:
        return (None,None)
    else:
        mi = L[0]
        ma = L[0]
        for l in L:
            if l < mi:
                mi = l
            elif l > ma:
                ma = l
        return (mi,ma)

# 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!')