# -*- coding: utf-8 -*-

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

L2 = []

for item in L1:

if isinstance(item, str):

L2.append(item)

L2 = [item.lower() for item in L2]

# 测试:

print(L2)

if L2 == ['hello', 'world', 'apple']:

print('测试通过!')

else:

print('测试失败!')