字典循环查询时不能进行删除操作，会报错！！！

不仅是字典，列表同样会。

例如：将dic字典中含有’k‘的键删除

dic = {'k1':'v1','k2':'v2','a3':'v3'}
for i in dic:
    if 'k' in i:
        del dic[i]
        print(dic)

输出报错：

它虽然删除了第一个，但是之后开始报错

{'k2': 'v2', 'a3': 'v3'}
Traceback (most recent call last):
  File "D:/PycharmProjects/untitled/day7/数据类型汇总.py", line 48, in <module>
    for i in dic:
RuntimeError: dictionary changed size during iteration

解决办法：将含有'k'的键值单独拿出来创建一个列表，再通过列表元素循环删除字典中的键；或者将不含有’k‘的键值重新创建一个新的字典

dic = {'k1':'v1','k2':'v2','a3':'v3'}

dic1 = {}
for i in dic.keys():
    if 'k' not in i:
       dic1 = dic1.setdefault(i,dic[i])
       print(dic1)

'''
li = []
for i in dic.keys():
    if 'k' in i:
        li.append(i)
for i1 in li:
    if 'k' in i1:
        del dic[i1]
print(dic)

'''