json

Posted 2021-01-20 Ethan

一、定义

• json全称：javascript object notation
• 前后端交互的枢纽：后端通过将程序产生的字典转化成json格式的json字符串(串)，然后通过网络传输，给到前端，前端解析json文件，完成数据交互

二、python字典与json字符串相互转换

1. python字典 ------> json字符串：dumps

• ensure_ascii：默认为True。如果ensure_ascii为False, 那么写入的字符串中可以包含非ASCII字符

import json

dic = {"name": "Tom", "age": 18, "hobby": "篮球", 1: False, 2: None}
s = json.dumps(dic, ensure_ascii=False)
print(s)  # {"name": "Tom", "age": 18, "hobby": "篮球", "1": false, "2": null}

 2. json字符串 ------> python字典：loads

s = \'{"name": "Tom", "age": 18, "hobby": "篮球", "1": false, "2": null}\'
dic = json.loads(s)
print(dic)   # {\'name\': \'Tom\', \'age\': 18, \'hobby\': \'篮球\', \'1\': False, \'2\': None}

 三、读、写json文件

1. dump

• 将python字典转换成json字符串，并写入文件中

• indent：缩进

import json

dic = {"name": "Tom", "age": 18, "hobby": "篮球", 1: False, 2: None}
f = open("1.json", "w", encoding="utf-8")  # 把对象打散成json写入到文件中
json.dump(dic, f, ensure_ascii=False, indent=4)
f.close()

结果：

2. load

• 读取json文件，并解析成字典

import json
f = open("1.json", encoding="utf-8")
dic = json.load(f)
f.close()
print(dic)  # {\'name\': \'Tom\', \'age\': 18, \'hobby\': \'篮球\', \'1\': False, \'2\': None}

 四、读、写多个json字符串

1. 问题

    我们可以向同一文件中写入多个json字符串,但是json文件中内容是一行内容。此时读取时无法读取。

import json

lst = [{"a": 1}, {"b": 2}, {"c": 3}]
f = open("2.json", "w")
for el in lst:
    json.dump(el, f)
f.close()

结果：

 

 

f = open("2.json")
dic = json.load(f)

结果：
json.decoder.JSONDecodeError: Extra data: line 1 column 9 (char 8)

 2. 解决方案

    改用dumps和loads，对每一行分别做处理

import json

lst = [{"a": 1}, {"b": 2}, {"c": 3}]

f = open("2.json", "w")
for el in lst:
    s = json.dumps(el) + "\\n"
    f.write(s)
f.close()

结果：

 

f = open("2.json")
for line in f:
    dic = json.loads(line.strip())
    print(dic)
f. close()

结果：
{\'a\': 1}
{\'b\': 2}
{\'c\': 3}

 五、json处理类

1. 将类转换成json字符串

import json


class Person(object):

    def __init__(self, name, age):
        self.name = name
        self.age = age


p = Person("Tom", 18)


def func(obj):
    return {"name": obj.name, "age": obj.age}


s = json.dumps(p, default=func)
print(s)  # {"name": "Tom", "age": 18}

2. 将json字符串赋给类

class Person(object):

    def __init__(self, name, age):
        self.name = name
        self.age = age


s = \'{"name": "Tom", "age": 18}\'

def func(dic):
    return Person(dic["name"], dic["age"])

p = json.loads(s, object_hook=func)
print(p.name, p.age)  # Tom  18