1.切片：利用切片操作，实现一个trim()函数，去除字符串首尾的空格，注意不要调用str的strip()方法：

def trim(s):
    print(s)
    if s[:1]!=' 'and s[-1:]!=' ':
        return s
    elif s[:1]==' ':
        return trim(s[1:]) #利用递归函数
        print(s[1:])
    else:
        return trim(s[:-1])
        print(s[:-1])
# 测试:

if trim('hello  ') != 'hello':
    print('test failed!')
elif trim('  hello') != 'hello':
    print('test failed!')
elif trim('  hello  ') != 'hello':
    print('test failed!')
elif trim('  hello  world  ') != 'hello  world':
    print('test failed!')
elif trim('') != '':
    print('test failed!')
elif trim('    ') != '':
    print('test failed!')
else:
    print('test successfully!')

2.迭代：请使用迭代查找一个list中最小和最大值，并返回一个tuple

def findMinAndMax(L):
    MIN=L[0]
    MAX=L[0]
    for i in L:
        if i<MIN:
            MIN=i
    for j in L:
        if j>MAX:
            MAX=j
    return (MIN,MAX)
           
# 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!')

3.列表生成式：请修改列表生成式，通过添加if语句保证列表生成式能正确地执行：

-- coding: utf-8 --

L1 = ['Hello', 'World', 18, 'Apple', None]

--测试数据--

print(L2)
if L2 == ['hello', 'world', 'apple']:
print('测试通过!')
else:
print('测试失败!')

--代码--：

def ListAndLower(s):
    L2=[i.lower() for i in s if (isinstance(i,str))]
    return L2
    

L1=['Hello','World',18,'Apple',None]#定义list L1

ListAndLower(L1)#调用函数

#测试
print(ListAndLower(L1))
if ListAndLower(L1) == ['hello', 'world', 'apple']:
    print('test successfully!')
else:
    print('test failed')

运行结果：

image.png