Type Hint ও Pydantic

name: str = "Rahim"
age: int = 26
price: float = 99.5
active: bool = True

def greet(name: str, times: int = 1) -> str:
    return ("হ্যালো " + name + "! ") * times

# collection (Python 3.9+ এ সরাসরি list[...], dict[...])
scores: list[int] = [90, 85]
prices: dict[str, int] = {"আম": 120}
location: tuple[float, float] = (23.8, 90.4)
tags: set[str] = {"food", "fast"}

def find_user(user_id: int) -> dict | None:     # dict অথবা None
    ...

user = find_user(5)
print(user["name"])       # ⚠ type checker সতর্ক করবে: user None হতে পারে

if user is not None:
    print(user["name"])   # ✓ এখন নিশ্চিত

from typing import Literal, Any, Callable, TypedDict

# নির্দিষ্ট কয়েকটা value
def set_theme(mode: Literal["light", "dark"]) -> None: ...
set_theme("blue")   # ⚠ type checker ধরবে

# function কে parameter হিসেবে
def retry(func: Callable[[], str], times: int) -> str: ...

# dict এর key গুলোর type ঠিক করা (JSON এর গঠন বোঝাতে)
class UserDict(TypedDict):
    id: int
    name: str
    email: str

# type এর নতুন নাম (alias)
type UserId = int
type JSON = dict[str, Any]

def first[T](items: list[T]) -> T | None:      # Python 3.12+ এর syntax
    return items[0] if items else None

x = first([1, 2, 3])        # type checker জানে x হলো int | None
y = first(["a", "b"])       # y হলো str | None

from typing import Protocol

class Notifier(Protocol):
    def send(self, to: str, message: str) -> None: ...

class SmsNotifier:                      # Notifier থেকে inherit করেনি
    def send(self, to: str, message: str) -> None:
        print(f"SMS → {to}: {message}")

def notify_customer(n: Notifier) -> None:
    n.send("017...", "Order confirmed")

notify_customer(SmsNotifier())          # ✓ চলবে, কারণ send() আছে

uv add --dev pyright
uv run pyright

src/app/orders.py:12:15 - error: "None" is not subscriptable
src/app/orders.py:20:9 - error: Argument of type "str" cannot be assigned to parameter "qty" of type "int"
2 errors

uv add pydantic "pydantic[email]"

from pydantic import BaseModel, Field, EmailStr, ValidationError


class Address(BaseModel):
    area: str
    city: str = "Dhaka"


class UserCreate(BaseModel):
    name: str = Field(min_length=2, max_length=50)
    email: EmailStr
    age: int = Field(ge=13, le=120)            # ১৩ থেকে ১২০
    phone: str = Field(pattern=r"^01[3-9]\d{8}$")   # বাংলাদেশি mobile নম্বর
    address: Address                           # nested model
    tags: list[str] = []


# সঠিক data
data = {
    "name": "Nusrat",
    "email": "nusrat@example.com",
    "age": "27",                 # string, কিন্তু Pydantic int এ বদলে নেবে
    "phone": "01712345678",
    "address": {"area": "Mirpur"},
}
user = UserCreate(**data)        # অথবা UserCreate.model_validate(data)
print(user.age + 1)              # 28, এখন int
print(user.address.city)         # Dhaka (default)
print(user.model_dump())         # আবার dict এ
print(user.model_dump_json())    # JSON string এ

try:
    UserCreate(name="A", email="not-email", age=8, phone="123", address={})
except ValidationError as e:
    print(e)

5 validation errors for UserCreate
name
  String should have at least 2 characters
email
  value is not a valid email address
age
  Input should be greater than or equal to 13
phone
  String should match pattern '^01[3-9]\d{8}$'
address.area
  Field required

from pydantic import BaseModel, field_validator, model_validator


class OrderCreate(BaseModel):
    items: list[str]
    coupon: str | None = None
    delivery_slot_start: int      # ঘণ্টা (0-23)
    delivery_slot_end: int

    @field_validator("coupon")
    @classmethod
    def normalize_coupon(cls, v: str | None) -> str | None:
        return v.strip().upper() if v else v

    @model_validator(mode="after")
    def check_slot(self) -> "OrderCreate":
        if self.delivery_slot_end <= self.delivery_slot_start:
            raise ValueError("Delivery এর শেষ সময় শুরুর পরে হতে হবে")
        return self

uv add pydantic-settings

from pydantic_settings import BaseSettings, SettingsConfigDict


class Settings(BaseSettings):
    model_config = SettingsConfigDict(env_file=".env")

    database_url: str
    redis_url: str = "redis://localhost:6379/0"
    jwt_secret: str
    debug: bool = False


settings = Settings()      # .env আর environment থেকে পড়বে, না পেলে error

DATABASE_URL=postgresql+asyncpg://app:secret@localhost:5432/notes
JWT_SECRET=change-me-in-production
DEBUG=true