from pydantic import BaseModel, Field, EmailStr
from datetime import datetime

class User(BaseModel):
    id: int
    name: str = Field(..., min_length=1, max_length=100)
    email: EmailStr
    created_at: datetime = Field(default_factory=datetime.now)
    is_active: bool = True

---

from pydantic import BaseModel, ConfigDict

class Product(BaseModel):
    model_config = ConfigDict(
        str_strip_whitespace=True,
        validate_assignment=True,
        use_enum_values=True,
        arbitrary_types_allowed=False
    )

    name: str
    price: float
    quantity: int = 0

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from pydantic import Field, field_validator
from typing import Annotated

class Item(BaseModel):
    # Field constraints
    sku: str = Field(pattern=r'^[A-Z]{3}-\d{4}$')
    price: float = Field(gt=0, le=10000)
    stock: int = Field(ge=0, default=0)

    # Annotated types (Pydantic v2)
    quantity: Annotated[int, Field(ge=1, le=100)]

    # Descriptions and examples
    description: str = Field(
        ...,
        description="Product description",
        examples=["High-quality widget"]
    )

    # Deprecated fields
    old_field: str | None = Field(None, deprecated=True)

    @field_validator('sku')
    @classmethod
    def validate_sku(cls, v: str) -> str:
        if not v.startswith('ABC'):
            raise ValueError('SKU must start with ABC')
        return v

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@model_serializer
def ser_model(self) -> dict:
    return {...}

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from pydantic import (
    BaseModel, EmailStr, HttpUrl, UUID4,
    FilePath, DirectoryPath, Json, SecretStr,
    PositiveInt, NegativeFloat, conint, constr
)
from typing import Literal
from pathlib import Path

class Example(BaseModel):
    # Email validation
    email: EmailStr

    # URL validation
    website: HttpUrl

    # UUID
    id: UUID4

    # File system paths
    config_file: FilePath
    data_dir: DirectoryPath

    # JSON string → parsed object
    metadata: Json[dict[str, str]]

    # Secret (won't print in logs)
    api_key: SecretStr

    # Constrained types
    age: PositiveInt
    balance: NegativeFloat
    username: constr(min_length=3, max_length=20, pattern=r'^[a-z]+$')
    code: conint(ge=1000, le=9999)

    # Literal types
    status: Literal['pending', 'approved', 'rejected']

from pydantic import GetCoreSchemaHandler, GetJsonSchemaHandler
from pydantic_core import core_schema
from typing import Any

class Color:
    def __init__(self, r: int, g: int, b: int):
        self.r, self.g, self.b = r, g, b

    @classmethod
    def __get_pydantic_core_schema__(
        cls, source_type: Any, handler: GetCoreSchemaHandler
    ) -> core_schema.CoreSchema:
        return core_schema.no_info_after_validator_function(
            cls.validate,
            core_schema.str_schema()
        )

    @classmethod
    def validate(cls, v: str) -> 'Color':
        if not v.startswith('#') or len(v) != 7:
            raise ValueError('Invalid hex color')
        r = int(v[1:3], 16)
        g = int(v[3:5], 16)
        b = int(v[5:7], 16)
        return cls(r, g, b)

class Design(BaseModel):
    primary_color: Color

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from pydantic import field_validator, model_validator

class Account(BaseModel):
    username: str
    password: str
    password_confirm: str

    @field_validator('username')
    @classmethod
    def username_alphanumeric(cls, v: str) -> str:
        if not v.isalnum():
            raise ValueError('must be alphanumeric')
        return v

    @field_validator('password')
    @classmethod
    def password_strong(cls, v: str) -> str:
        if len(v) < 8:
            raise ValueError('must be at least 8 characters')
        if not any(c.isupper() for c in v):
            raise ValueError('must contain uppercase letter')
        return v

    # Validate multiple fields
    @field_validator('username', 'password')
    @classmethod
    def not_empty(cls, v: str) -> str:
        if not v or not v.strip():
            raise ValueError('must not be empty')
        return v.strip()

from pydantic import model_validator
from typing import Self

class DateRange(BaseModel):
    start_date: datetime
    end_date: datetime

    @model_validator(mode='after')
    def check_dates(self) -> Self:
        if self.end_date < self.start_date:
            raise ValueError('end_date must be after start_date')
        return self

class Order(BaseModel):
    items: list[str]
    total: float
    discount: float = 0

    @model_validator(mode='before')
    @classmethod
    def calculate_total(cls, data: dict) -> dict:
        # Pre-processing before validation
        if isinstance(data, dict) and 'total' not in data:
            data['total'] = len(data.get('items', [])) * 10.0
        return data

from pydantic import model_validator, ValidationInfo

class Config(BaseModel):
    env: Literal['dev', 'prod']
    debug: bool = False

    @model_validator(mode='wrap')
    @classmethod
    def validate_config(cls, values: Any, handler, info: ValidationInfo):
        # Call default validation
        result = handler(values)

        # Post-validation logic
        if result.env == 'prod' and result.debug:
            raise ValueError('debug cannot be True in production')

        return result

from pydantic import BaseModel, ConfigDict, ValidationError

count: int
price: float

undefined

from pydantic import BaseModel
from typing import ForwardRef

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from pydantic import BaseModel
from typing import Generic, TypeVar

T = TypeVar('T')

class Response(BaseModel, Generic[T]):
    success: bool
    data: T
    message: str = ''

class User(BaseModel):
    id: int
    name: str

def add(self, item: T) -> None:
    self.items.append(item)

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from pydantic import BaseModel, Field, field_serializer

class Article(BaseModel):
    title: str
    content: str
    tags: list[str]
    metadata: dict[str, Any] = {}

    # Serialization customization
    @field_serializer('tags')
    def serialize_tags(self, tags: list[str]) -> str:
        return ','.join(tags)

article = Article(
    title='Pydantic Guide',
    content='...',
    tags=['python', 'validation']
)

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from datetime import datetime
from pydantic import BaseModel, field_serializer

class Event(BaseModel):
    name: str
    timestamp: datetime

    @field_serializer('timestamp')
    def serialize_dt(self, dt: datetime) -> str:
        return dt.isoformat()

event = Event(name='Deploy', timestamp=datetime.now())

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from pydantic import model_serializer

class User(BaseModel):
    id: int
    username: str
    password: SecretStr

    @model_serializer
    def ser_model(self) -> dict[str, Any]:
        return {
            'id': self.id,
            'username': self.username,
            # Never serialize password
        }

user = User(id=1, username='alice', password='secret123')
assert 'password' not in user.model_dump()

from pydantic_settings import BaseSettings, SettingsConfigDict
from pydantic import Field

class AppSettings(BaseSettings):
    model_config = SettingsConfigDict(
        env_file='.env',
        env_file_encoding='utf-8',
        env_prefix='APP_',
        case_sensitive=False
    )

    # Environment variables
    database_url: str
    redis_url: str = 'redis://localhost:6379'
    secret_key: SecretStr
    debug: bool = False

    # Nested settings
    class SMTPSettings(BaseModel):
        host: str
        port: int = 587
        username: str
        password: SecretStr

    smtp: SMTPSettings

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from functools import lru_cache

class Settings(BaseSettings):
    environment: Literal['dev', 'staging', 'prod'] = 'dev'
    database_url: str
    api_key: SecretStr

    model_config = SettingsConfigDict(
        env_file='.env',
        extra='ignore'
    )

    @property
    def is_production(self) -> bool:
        return self.environment == 'prod'

@lru_cache
def get_settings() -> Settings:
    return Settings()

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from fastapi import FastAPI, HTTPException
from pydantic import BaseModel, EmailStr

app = FastAPI()

class UserCreate(BaseModel):
    username: str = Field(min_length=3, max_length=50)
    email: EmailStr
    password: str = Field(min_length=8)

class UserResponse(BaseModel):
    id: int
    username: str
    email: EmailStr

    model_config = ConfigDict(from_attributes=True)

@app.post('/users', response_model=UserResponse)
def create_user(user: UserCreate):
    # FastAPI auto-validates request body
    # Returns only fields in UserResponse (password excluded)
    return UserResponse(
        id=1,
        username=user.username,
        email=user.email
    )

from pydantic import BaseModel, Field
from fastapi import Query

class PaginationParams(BaseModel):
    skip: int = Field(0, ge=0)
    limit: int = Field(10, ge=1, le=100)

class SearchParams(BaseModel):
    q: str = Field(..., min_length=1)
    category: str | None = None
    sort_by: Literal['date', 'relevance'] = 'relevance'

@app.get('/search')
def search(params: SearchParams = Query()):
    return {'query': params.q, 'sort': params.sort_by}

class DetailedUser(BaseModel):
    id: int
    username: str
    email: EmailStr
    created_at: datetime
    last_login: datetime | None

@app.get('/users/{user_id}', response_model=DetailedUser)
def get_user(user_id: int, include_dates: bool = False):
    user = DetailedUser(
        id=user_id,
        username='alice',
        email='alice@example.com',
        created_at=datetime.now(),
        last_login=None
    )

    if not include_dates:
        return user.model_dump(exclude={'created_at', 'last_login'})
    return user

from sqlalchemy import Column, Integer, String, DateTime
from sqlalchemy.orm import DeclarativeBase
from pydantic import BaseModel, ConfigDict

class Base(DeclarativeBase):
    pass

id = Column(Integer, primary_key=True)
username = Column(String(50), unique=True)
email = Column(String(100))
created_at = Column(DateTime, default=datetime.utcnow)

id: int
username: str
email: EmailStr
created_at: datetime

undefined

from pydantic import BaseModel

class UserBase(BaseModel):
    username: str
    email: EmailStr

class UserCreate(UserBase):
    password: str

class UserUpdate(BaseModel):
    username: str | None = None
    email: EmailStr | None = None
    password: str | None = None

class UserInDB(UserBase):
    model_config = ConfigDict(from_attributes=True)

    id: int
    created_at: datetime
    password_hash: str

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from django.db import models
from pydantic import BaseModel, field_validator

title: str = Field(max_length=200)
content: str
published: bool = False

@field_validator('content')
@classmethod
def validate_content(cls, v: str) -> str:
    if len(v) < 100:
        raise ValueError('Content too short')
    return v

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from pydantic import computed_field

class Rectangle(BaseModel):
    width: float
    height: float

    @computed_field
    @property
    def area(self) -> float:
        return self.width * self.height

    @computed_field
    @property
    def perimeter(self) -> float:
        return 2 * (self.width + self.height)

rect = Rectangle(width=10, height=5)
assert rect.area == 50
assert rect.perimeter == 30

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from pydantic import BaseModel, field_validator, ValidationError
from pydantic_core import PydanticCustomError

class StrictUser(BaseModel):
    username: str
    age: int

    @field_validator('username')
    @classmethod
    def validate_username(cls, v: str) -> str:
        if len(v) < 3:
            raise PydanticCustomError(
                'username_too_short',
                'Username must be at least 3 characters',
                {'min_length': 3, 'actual_length': len(v)}
            )
        return v

    @field_validator('age')
    @classmethod
    def validate_age(cls, v: int) -> int:
        if v < 18:
            raise PydanticCustomError(
                'underage',
                'User must be at least 18 years old',
                {'age': v, 'minimum_age': 18}
            )
        return v

undefined

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from pydantic import BaseModel, ConfigDict

class OptimizedModel(BaseModel):
    model_config = ConfigDict(
        # Validate assignment only when needed
        validate_assignment=False,

        # Disable validation for internal use
        validate_default=False,

        # Use slots for memory efficiency
        # (Not available in Pydantic v2 BaseModel directly)
    )

    data: list[int]

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from pydantic import BaseModel, Field

class Product(BaseModel):
    """Product model for catalog"""

    id: int = Field(description="Unique product identifier")
    name: str = Field(description="Product name", examples=["Widget"])
    price: float = Field(gt=0, description="Price in USD")
    tags: list[str] = Field(default=[], description="Product tags")