跳转到主要内容
eLearner.app
模块 8 · 第 1 课（共 4）课程中的29/36~10 min
模块课程（1/4）

JSON：序列化和解析

JSON is the most widespread data exchange format. The json module in the standard library handles it natively.

From Python to JSON: dumps

json.dumps(object) serializes a Python object into a JSON string.

Python
import json

dati = {"nome": "Ada", "anni": 36, "skills": ["python", "matematica"]}
json.dumps(dati)
# '{"nome": "Ada", "anni": 36, "skills": ["python", "matematica"]}'

json.dumps(dati, indent=2, sort_keys=True)
# multi-line formatted string, keys sorted

From JSON to Python: loads

json.loads(string) parses a JSON string and returns Python objects.

Python
testo = '{"nome": "Ada", "anni": 36}'
d = json.loads(testo)
d["nome"]    # 'Ada'
type(d)      # <class 'dict'>

Type mapping

JSONPython
objectdict
arraylist
stringstr
numberint / float
trueTrue
falseFalse
nullNone

From file: dump / load

Python
with open("config.json", "w") as f:
    json.dump(dati, f, indent=2)

with open("config.json") as f:
    dati = json.load(f)

Without the trailing "s" they work on files (file-like), with the "s" on strings.

Non-serializable types: default

datetime, set, your custom classes are not serializable by default:

Python
import datetime, json
json.dumps({"ora": datetime.datetime.now()})
# TypeError: Object of type datetime is not JSON serializable

You can pass a default function that tells how to transform them:

Python
def converti(obj):
    if isinstance(obj, datetime.datetime):
        return obj.isoformat()
    if isinstance(obj, set):
        return list(obj)
    raise TypeError(f"non serializzabile: {type(obj)}")

json.dumps({"ora": datetime.datetime.now()}, default=converti)

JSON and file operations

The standard library also provides json.dump() and json.load() (without the 's') to write and read JSON data directly to and from files, pairing naturally with context managers:

Python
with open("data.json", "w") as f:
    json.dump(data, f)

Try it

锻炼#python.m8.l1.e1
尝试：0加载中...

Given `data = {'nome': 'Ada', 'anni': 36}`, serialize it to JSON with indent=2 and assign to the variable `json_str`. Evaluate `json_str`.

正在加载编辑器...
显示提示

json.dumps(data, indent=2)

3 次尝试后可用的解决方案

Review exercise

锻炼#python.m8.l1.e2
尝试：0加载中...

Given the JSON string s = '[{"nome": "a", "v": 1}, {"nome": "b", "v": 2}]', parse it with json.loads into data and compute the sum of the 'v' values in total. Evaluate total.

正在加载编辑器...
显示提示

json.loads returns a list of dicts.

3 次尝试后可用的解决方案

Additional challenge

锻炼#python.m8.l1.e3
尝试：0加载中...

Given the JSON string `json_data = '{"name": "Alice", "age": 30}'`, decode it into a Python dictionary using `json.loads`. Extract the value associated with the `'name'` key and store it in `user_name`. Finally, evaluate `user_name`.

正在加载编辑器...
显示提示

Use json.loads(json_data) to decode, then access via data['name'].

3 次尝试后可用的解决方案