④ 数据存储

json文件处理

1.json支持的数据格式

字典：使用花括号

数组：使用方括号

整型、浮点型、bool型、null类型

字符串类型：必须用双引号

本质：json就是一个字符串

2.字典和列表转json

# encoding:utf-8
import json

persons = [
    {
        'username': "xiao",
        "age": 20,
        "country": "china"
    }
]
json_str = json.dumps(persons) //dumps方法转换

print(type(json_str))
print(json_str)
结果：
<class 'str'>
[{"username": "xiao", "age": 20, "country": "china"}]

输出到文件

# encoding:utf-8
import json

persons = [
    {
        'username': "xiao",
        "age": 20,
        "country": "china"
    }
]
with open('person.json', 'w', encoding='utf-8') as f:
    json.dump(persons, f, ensure_ascii=False)
// dump方法存储到文件中   
// ensure_ascii=默认为ture 转换为ASCII码，FALSE时需要指定encoding编码

3.将json字符串load成Python对象

# encoding:utf-8
import json

json_str = '[{"username": "小灰灰", "age": 20, "country": "china"}]'
persons = json.loads(json_str) // laods方法
print(type(persons))
for person in persons:
    print(person)

从文件读取

# encoding:utf-8
import json

with open('person.json', 'r', encoding='utf-8') as f:
    persons = json.load(f) // load方法
    print(type(persons))
    for person in persons:
        print(person)

CSV文件

1.读取csv文件

方法一：

# encoding:utf-8
import csv

with open('stoc.csv', 'r') as f:
	next(reader) // 跳过第一行
    //reader方法是一个迭代器
    reader = csv.reader(f)
    for x in reader:
        print(x)

方法二：

# encoding:utf-8
import csv

with open('stoc.csv', 'r') as f:
	reader = csv.DictReader(f) //返回字典格式，且不会包含第一行
	
	

2.写入csv文件

方法一：

# encoding:utf-8
import csv

headers = ['username', 'age', 'height']
values = [
    ('张三', 18, 180),
    ('王二', 20, 178),
    ('李四', 20, 182)
]
with open('test.csv', 'w', encoding='utf-8',newline='') as f:
    write = csv.writer(f)
    write.writerow(headers) //写入标题
    write.writerows(values) //写入多行

方法二：

# encoding:utf-8
import csv

headers = ['username', 'age', 'height']
values = [
    {'username': '张三', 'age': 18, 'height': 180},
    {'username': '王二', 'age': 20, 'height': 178},
    {'username': '李四', 'age': 20, 'height': 182},
]
with open('test.csv', 'w', encoding='utf-8', newline='') as f:
    write = csv.DictWriter(f, headers)
    write.writeheader() //表头标题需要用writeheader方法
    write.writerows(values)