python学习笔记7---数据存储

dump成json字符串以及编码问题

import json

persons = [
{
'username':"蔡",
'age':18
},
{
'username':"时",
'age':19
}
]
with open('person.json','w') as fp:
    json.dump(persons,fp,ensure_ascii=False)# json在dump时只能存放ascii字符，所以用ensure_ascii=False关闭这个特性
    

只有基本数据类型才能转换成JSON格式的字符串，即：int、float、str、list、dict、tuple

load成python对象

import json
with open('person.json','r',encoding='utf-8') as fp:
    persons = json.load(fp)
    print(type(persons))  #list
    for person in persons:
        print(person)

读取csv文件的两种方式

import csv
 
with open('stock.csv','r') as fp:
    # reader是迭代器
    reader = csv.reader(fp)
    next(reader) # 跳过第0行，即不显示标题
    for x in reader:
        name=x[3]
        volumn = x[-1]
        print({'name':'name','volumn':volumn})

import csv
with open('stock.csv','r') as fp:
    reader= csv.DictReader(fp)
    for x in reader:
        value = {"name":x['secShortName'],'volumn':x['turnoverVol']}
        print(value)

写入csv文件的两种方式

方法①

import csv
headers = ['username','age']
values = [
('张三',18)
('李四',20)
]
# newline去掉每一行中隔的空行
with open('classroom.csv','w',encoding='utf-8',newline='') as fp:
    writer = csv.writer(fp)
    writer.writerow(headers)
    writer.writerrows(values)   
    

方法②

import csv
headers = ['username','age']
values=[
{'username':'张三','age':18},
{'uesername':'李四',‘age’:19}
]

with open('classroom.csv','w',encoding='utf-8',newline='') as fp:
    writer=csv.DictWriter(fp,headers)
    # 写入表头时要调用writerheader方法
    writer.writerheader()
    writer.writerows(values)