起因：

需要提出字典对象中value为空的key

def test_dic(dic):for x in dic.keys():if dic[x] is None:dic.pop(x)return dict_dic = {'a1': None, 'b1': 1}
print(test_dic(t_dic))

运行后报错：RuntimeError: dictionary changed size during iteration

在遍历时不能修改字典元素，修改遍历的方式：

def test_dic(dic):for x in list(dic.keys()):if dic[x] is None:dic.pop(x)return dict_dic = {'a1': None, 'b1': 1}
print(test_dic(t_dic))

运行成功，成功打印了：{'b1': 1}