如何实现文件操作

[ruhangs]

print("1: 请录入学生信息 \n2: 请输入需要删除的学生学号 \n3: 请输出需要查询的学生学号 \n0: 退出")
str = []
while True:
x = input("请输入您的选择：")
if x.isdigit():
x = int(x)
if x == 1:
stunum = input("请输入学生学号:")
name = input("请输入姓名:")
type = input("请输入英语类别:")
grade = input("请输入学生成绩：")
dict = {}
dict['stunum'] = stunum
dict['name'] = name
dict['type'] = type
dict['grade'] = grade
print(dict)
str.append(dict)
print(str)
print("如需继续录入学生信息请选择[1]")
elif x == 2:
stunum1 = input("请输入要删除学生信息的学号：")
find_flag = False
for l in str:
if l['stunum'] == stunum1:
find_flag = True
str.remove(l)
break
if find_flag:
print("已删除！")
print(str)
else:
print("学号不存在！")
elif x == 3:
stunum2 = input("请输入要查询学生信息的学号：")
find_flag = 0
for i in str:
if i['stunum'] == stunum2:
find_flag = 1
break
if find_flag == 1:
print("学号:",i['stunum']," 姓名:",i['name']," 英语类型:",i['type']," 成绩:",i['grade'])
else:
print("学号不存在！")
elif x == 0:
break
else:
print("输入有误！请重新输入：")
continue
else:
print("输入有误！请重新输入：")