字典的坑

1.在循环字典时不能删除键值对，否刚会报错

删除方法：

方法一　　

dic = {'a1':'aaa','a2':'bbb','b1':'ccc'}
dic1 = {}

for i in dic:
    if 'a' not in i:
        dic1.setdefault(i,dic[i]}
dic = dic1
print(dic)            //{'b1':'ccc'}

 方法二：

dic = {'a1':'aaa','a2':'bbb','b1':'ccc'}
l = []
for i in dic:
    if 'a' in i:
        l.append(i)
for i in l:
    del dic[i]
print(dic)         // {'b1':'ccc'}