JSON, CSV и сериализация

import json

order = {"id": 42, "клиент": "Анна", "товары": ["чай", "кофе"], "оплачен": True, "скидка": None}

text = json.dumps(order)                                   # объект → строка
print(text)
print(json.dumps(order, ensure_ascii=False, indent=2))     # кириллица как есть, с отступами

data = json.loads('{"id": 1, "tags": ["a", "b"], "price": 9.5, "active": false}')   # строка → объект
print(data, type(data["tags"]))

print(json.loads(json.dumps({1: "a", "t": (1, 2)})))       # ключ стал строкой, кортеж — списком

import json, tempfile
from pathlib import Path

path = Path(tempfile.mkdtemp()) / "config.json"
with open(path, "w", encoding="utf-8") as f:
    json.dump({"debug": True, "db": {"host": "localhost", "port": 5432}}, f, ensure_ascii=False, indent=2)

with open(path, encoding="utf-8") as f:
    config = json.load(f)
print(config["db"]["port"])

try:
    json.loads("{'single': 'quotes'}")                     # в JSON только двойные кавычки
except json.JSONDecodeError as e:
    print("JSONDecodeError:", e)

import json
from dataclasses import dataclass, asdict
from datetime import datetime, date
from decimal import Decimal
from uuid import UUID, uuid4

@dataclass
class Item:
    title: str
    price: Decimal

def encode(value):                       # вызывается для всего, что json не знает
    if isinstance(value, (datetime, date)):
        return value.isoformat()
    if isinstance(value, (Decimal, UUID)):
        return str(value)
    if hasattr(value, "__dataclass_fields__"):
        return asdict(value)
    raise TypeError(f"{type(value).__name__} не сериализуется в JSON")

payload = {"id": UUID("12345678-1234-5678-1234-567812345678"),
           "created": datetime(2026, 10, 25, 14, 30), "item": Item("Книга", Decimal("590.00"))}
text = json.dumps(payload, default=encode, ensure_ascii=False)
print(text)

def decode(obj):                         # вызывается для каждого словаря при чтении
    if "created" in obj:
        obj["created"] = datetime.fromisoformat(obj["created"])
    return obj

back = json.loads(text, object_hook=decode, parse_float=Decimal)
print(type(back["created"]).__name__, back["item"])

import csv, io

raw = 'name,city,salary\nАнна,"Москва, центр",120000\nБоря,Казань,95000\n"Вера ""Ви""",Сочи,110000\n'

print(raw.splitlines()[1].split(","))           # наивный split ломается на запятой в кавычках

for row in csv.reader(io.StringIO(raw)):
    print(row)

for row in csv.DictReader(io.StringIO(raw)):    # строка → словарь по заголовку
    print(row["name"], int(row["salary"]) // 1000, "тыс.")

import csv, tempfile
from pathlib import Path

rows = [{"id": 1, "name": "Анна", "note": "любит, кофе"}, {"id": 2, "name": "Боря", "note": 'сказал "привет"'}]
path = Path(tempfile.mkdtemp()) / "users.csv"

with open(path, "w", newline="", encoding="utf-8") as f:     # newline="" — обязательно для csv
    writer = csv.DictWriter(f, fieldnames=["id", "name", "note"])
    writer.writeheader()
    writer.writerows(rows)

print(path.read_text(encoding="utf-8"))

with open(path, newline="", encoding="utf-8") as f:
    print([r["note"] for r in csv.DictReader(f)])           # всё вернулось как было

import pickle
from collections import Counter

data = {"counter": Counter("hello"), "tuple": (1, 2), "set": {3, 4}}
blob = pickle.dumps(data)
print(len(blob), "байт")
print(pickle.loads(blob))

import tomllib

config = tomllib.loads('''
[project]
name = "shop"
version = "1.0.0"
dependencies = ["fastapi>=0.110"]

[tool.ruff]
line-length = 100
''')
print(config["project"]["name"], config["tool"]["ruff"]["line-length"])