# 1 编写 tail -f a.txt |grep 'error' |grep '404'命令，周一默写

# import time

# def tail(filepath,encoding='utf-8'):

#     with open(filepath,encoding=encoding)as f:

#         f.seek(0,2)

#         while True:

#             line=f.readline()

#             if line:

#                 yield line

#             else:

#                 time.sleep(0.5)

# def grep(lines,pattern):

#     for line in lines:

#         if pattern in line:

#             # print(line)

#             yield line

# g=tail('a.txt')

# g2=grep(g,'error')

# g3=grep(g2,'404')

# for i in g3:

#     print(i)

# 2 文件a.txt内容

# apple 10 3

# tesla 100000 1

# mac 3000 2

# lenovo 30000 3

# chicken 10 3

# with open('a.txt','w',encoding='utf-8')as f:

#     f.write('apple 10 3\ntesla 100000 1\nmac 3000 2\nlenovo 30000 3\nchicken 10 3')

# 要求使用列表解析，从文件a.txt中取出每一行，做成下述格式

# [{‘name’:'apple','price':10,'count':3},{...},{...},...]

# with open('a.txt', 'r', encoding='utf-8')as f:

    # print([{'name':line.strip().split()[0],'price':line.strip().split()[1],'count':line.strip().split()[2]} for line in f])

    # for i in [{'name':line.strip().split()[0],'price':line.strip().split()[1],'count':line.strip().split()[2]} for line in f]:

    #     print(i)

# 3 格式与2一样，但只保留价格大于1000的商品信息

# with open('a.txt',encoding='utf-8')as f:

#     for i in [{'name':line.strip().split()[0],'price':line.strip().split()[1],'count':line.strip().split()[2]} for line in f]:

#         if int(i['price'])>1000:

#             print(i)

# 4 周末大作业（见图）：

#     只实现作业要求的查询功能

#     增加，删除，修改功能为选做题