3
实验楼楼赛第3期-Python-题解
source link: https://changkun.de/blog/posts/%E5%AE%9E%E9%AA%8C%E6%A5%BC%E6%A5%BC%E8%B5%9B%E7%AC%AC3%E6%9C%9F-python-%E9%A2%98%E8%A7%A3/
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因对 Python 感兴趣，于是早上吃早饭时看看。题目相对比较简单，最后一题代码写得比较随意。原本打算交上去测试一下，可惜海外党使用环境实在是卡得惨不忍睹，没办法写敲那么多代码上去。
题目：https://www.shiyanlou.com/contests/lou3/challenges
题目1: 存储学习记录
出现的问题:
- sqlite url schema 错误
- 外键设置错误
- 外键重复设置
解决方法:
- line 10:
sqlite://改为sqlite:/// - line 22:
backref='user'改为backref='course' - 表设计为一对多的外键，故注释掉 line 28 & line 30
题目2: 追踪课程更新
出现的问题:
- 缺少 object 基类
- 缺少子类初始化
- @property 方法访问错误
- typename 缺少参数
- 浅拷贝错误
解决方法:
- line 5: 改为
class Course(object) - line 21: 给
typename传递参数 self - line 28: 替换为
super(BootcampCourse, self).__init__(name, True, lab_count) - line 37: 改为调用
self.lab_count - line 29: 改为调用
copy.deepcopy
题目3: 修复 Internal Server Error
出现的问题:
- filter_by 用法错误
- html 模板错误
解决方法:
- app/main/views.py line 34:
filter_by(id=id).first_or_404() - app/templates/todolist.html line 4:
for('static', filename='js/todolist.js') - app/templates/todolist.html line 9:
{{todolist.title|title}}
题目4: NoSQL 的艺术
潜在的问题:
- 从 bash 中读入的值为字符串
- mongodb 的 aggregate pipeline 操作
- sort 结果搜索: mongodb 的 aggregate 操作找了半天实在没找到如何从操作结果的 cursor 拿到排名，只得做如下妥协处理，读者可继续探究
# TODO: return the rank of user_id
user_id = int(user_id)
results = contests.aggregate([
{
'$group': {
'_id': '$user_id',
'sum_score': {'$sum': '$score'},
'sum_time': {'$sum': '$submit_time'}
}
},
{
'$sort': {
'sum_score': -1,
'sum_time': -1
}
}
])
# CRISES: id_list may cause large memory consumption
id_list = [int(value['_id']) for value in results]
# INPROVEMENTS: could use binary search
try: return id_list.index(user_id)+1
except: return 0
题目5: 增加服务器管理功能
潜在的问题:
- 异常处理方式: 异常处理的部分原题目似乎并未写指示清楚, 这里用直接抛出 ScriptError 异常做处理
- csv 文件处理: 虽然其实并不是 csv 格式，但由于带空格的形式可以视为 csv 文件进行处理; 另一方面文件操作似乎并不支持单独一行的处理操作?
- 重复添加操作判断: 重复添加的判断逻辑应为: 当 hostip 和 user 同时相同时，则不能添加，否则可添加。
- 命令行参数处理: 最初决定使用 argparse 处理命令行参数，扫文档扫了半天没搞明白怎么添加 subparameter requirement，google 了一阵也很奇怪，最后还是决定直接暴力解包判断了
import sys
import csv
class ScriptError(Exception):
def __init__(self, value):
self.value = value
def __str__(self):
return repr('ERROR:'+self.value)
def listinfo():
with open('serverinfo', 'rb') as csvfile:
reader = csv.reader(csvfile, delimiter=' ')
for row in reader:
print ' '.join(row)
def addinfo(hostip, user, password):
with open('serverinfo', 'r+') as csvfile:
reader = csv.reader(csvfile, delimiter=' ')
contents = []
new = [hostip, user]
for row in reader:
contents.append([row[0], row[1]])
if new not in contents:
writer = csv.writer(csvfile, delimiter=' ')
writer.writerow([hostip, user, password])
else:
raise ScriptError('user exists')
def deleteinfo(hostip):
f = open('serverinfo', 'r')
lines = f.readlines()
f.close()
f = open('serverinfo', 'w')
for line in lines:
if hostip not in line:
f.write(line)
f.close()
def main():
if len(sys.argv) < 2:
print """
Usage:
======
python server.py [add|delete|list]
add: add info, required parameter below
-h hostip
-u user
-p password
delete: delete info, required parameter below
-h hostip
list:list all info
"""
elif sys.argv[1] == 'add':
if (sys.argv[2] == '-h' or sys.argv[2] == 'hostip') and \
(sys.argv[4] == '-u' or sys.argv[4] == 'user') and \
(sys.argv[6] == '-p' or sys.argv[6] == 'password') and \
len(sys.argv) == 8:
addinfo(sys.argv[3], sys.argv[5], sys.argv[7])
else:
raise ScriptError('argument error')
elif sys.argv[1] == 'delete':
if (sys.argv[2] == '-h' or sys.argv[2] == 'hostip') and len(sys.argv) == 4:
deleteinfo(sys.argv[3])
else:
raise ScriptError('argument error')
elif sys.argv[1] == 'list':
listinfo()
else: raise ScriptError('no such option')
if __name__ == '__main__':
main()
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