数据类与 Pydantic：字段声明之后，谁来校验

from dataclasses import dataclass

@dataclass
class Device:
    name: str
    volume: int = 50

Device(name="bedroom-01", volume=80)   # 干净利落

device = Device(name="", volume=99999)      # 空名字、音量爆表，照样构造成功
device = Device(name="客厅设备", volume="很响")  # 类型注解是 str/int，也没人拦
print(device.volume, type(device.volume))

很响 <class 'str'>

pip install pydantic

from pydantic import BaseModel

class Device(BaseModel):
    name: str
    volume: int = 50

d = Device(name="bedroom-01", volume="80")   # 注意：传的是字符串
print(d.volume, type(d.volume))

80 <class 'int'>

Device(name="bedroom-01", volume="很响")

Traceback (most recent call last):
  ...
pydantic_core._pydantic_core.ValidationError: 1 validation error for Device
volume
  Input should be a valid integer, unable to parse string as an integer [type=int_parsing, input_value='很响', ...]

from typing import Annotated
from pydantic import BaseModel, Field

Volume = Annotated[int, Field(ge=0, le=100)]

class Device(BaseModel):
    name: Annotated[str, Field(min_length=1, max_length=32)]
    volume: Volume = 50
    tags: list[str] = []

Device(name="bedroom-01", volume=150)

pydantic_core._pydantic_core.ValidationError: 1 validation error for Device
volume
  Input should be less than or equal to 100 [type=less_than_equal, input_value=150, ...]

from pydantic import BaseModel, field_validator

class Device(BaseModel):
    name: str

    @field_validator("name")
    @classmethod
    def name_must_have_prefix(cls, v: str) -> str:
        if not v.startswith("room-"):
            raise ValueError("设备名必须以 room- 开头")
        return v

from datetime import datetime
from pydantic import BaseModel, ConfigDict

class Device(BaseModel):
    model_config = ConfigDict(from_attributes=True)   # 允许从 ORM 对象读属性
    name: str
    volume: int
    created_at: datetime

d = Device(name="bedroom-01", volume=80, created_at=datetime(2026, 9, 28, 12, 0))
print(d.model_dump())          # datetime 仍是 datetime 对象
print(d.model_dump(mode="json"))  # datetime 变 ISO 字符串
print(d.model_dump_json())

{'name': 'bedroom-01', 'volume': 80, 'created_at': datetime.datetime(2026, 9, 28, 12, 0)}
{'name': 'bedroom-01', 'volume': 80, 'created_at': '2026-09-28T12:00:00'}
{"name":"bedroom-01","volume":80,"created_at":"2026-09-28T12:00:00"}

from pydantic import BaseModel, ConfigDict
from pydantic.alias_generators import to_camel

class APIResponse(BaseModel):
    model_config = ConfigDict(
        alias_generator=to_camel,   # user_id -> userId 自动生成别名
        populate_by_name=True,      # 两个字段名都接受（内部代码用 snake_case）
        str_strip_whitespace=True,  # 字符串自动去首尾空白
    )
    user_id: int
    user_name: str

resp = APIResponse.model_validate_json('{"userId": 1, "userName": "mia"}')
print(resp.user_name)               # mia
print(resp.model_dump(by_alias=True))   # 序列化回驼峰：{'userId': 1, 'userName': 'mia'}

import attrs

@attrs.define
class User:
    name: str = attrs.field(validator=attrs.validators.min_len(2))
    email: str = attrs.field()

    @email.validator
    def _check_email(self, attribute, value):
        if "@" not in value:
            raise ValueError("邮箱格式不合法")

@attrs.define
class Config:
    port: int = attrs.field(converter=int, default=8080)   # "8080" 也能进来
    debug: bool = attrs.field(converter=lambda x: str(x).lower() == "true", default=False)

print(Config(port="9000").port)    # 9000 —— converter 在赋值前自动转型

from dataclasses import dataclass, field

@dataclass
class Device:
    tags: list[str] = field(default_factory=list)   # 每个实例一份新列表

@dataclass
class Base:
    name: str            # 无默认

@dataclass
class Child(Base):
    level: int = 1       # 有默认

TypeError: non-default argument 'name' follows default argument

@dataclass(frozen=True)
class Point:
    x: float
    y: float
    norm: float = 0.0

    def __post_init__(self):
        object.__setattr__(self, "norm", (self.x ** 2 + self.y ** 2) ** 0.5)

from pydantic import TypeAdapter

devices = TypeAdapter(list[Device]).validate_python(raw_rows)