补充
.join用"" 连接列表返回字符串
s = "".join([‘ab’, ‘bb’, ‘cc’]) 迭代便利
print(s)
‘aa_bb_cc’

s = “_”.join(“abc”) 迭代便利
print(s)
‘a_b_c’

.split("") 用""分割

dic = dict.fromkeys(‘abc’, ‘aaa’)和原来的字典没有关系 生成新字典 直接用类名访问
print(dic)
{‘a’: ‘aaa’,‘b’: ‘aaa’,‘c’: ‘aaa’}

for循环中不可以删除被循环的列表和字典
列表删不全
字典不可以在循环中改变长度会报错
lst = [1,2,3,4,5]
lst1 = []
for i in lst:
lst1.append(i)
for i in lst1:
lst.remove(i)