自定义数据类型与设置

Welcome to Custom Types!

`Annotated` for Custom Validation

Crafting a `CapitalizedString`

Using Your Custom Type

from typing import Annotated
from pydantic import BaseModel, BeforeValidator, ValidationError

def validate_capitalized(v: str) -> str:
    if not isinstance(v, str):
        raise TypeError("String required")
    if v and not v[0].isupper():
        raise ValueError("Must start with uppercase")
    return v

CapitalizedString = Annotated[str, BeforeValidator(validate_capitalized)]

class Product(BaseModel):
    name: CapitalizedString
    price: float

if __name__ == "__main__":
    try:
        product1 = Product(name="Laptop", price=1200.50)
        print(f"Product: {product1.name}")

        # This will raise a ValidationError
        # product2 = Product(name="keyboard", price=75.00)
    except ValidationError as e:
        print(f"Validation Error: {e}")

Manage Settings with `BaseSettings`

Default Settings in Action

from pydantic_settings import BaseSettings

class AppConfig(BaseSettings):
    app_name: str = "My FastAPI App"
    debug_mode: bool = False
    version: str = "1.0.0"

if __name__ == "__main__":
    settings = AppConfig()
    print(f"App Name: {settings.app_name}")
    print(f"Debug Mode: {settings.debug_mode}")
    print(f"Version: {settings.version}")

Loading from Environment Variables

import os
from pydantic_settings import BaseSettings

class AppConfig(BaseSettings):
    app_name: str = "Default App"
    database_url: str = "sqlite:///./test.db"

if __name__ == "__main__":
    print("--- Without env var ---")
    settings_default = AppConfig()
    print(f"App Name: {settings_default.app_name}")

    # Simulate setting an environment variable
    os.environ["APP_NAME"] = "Production App"
    os.environ["DATABASE_URL"] = "postgresql://user:pass@host:5432/db"

    print("\n--- With env var ---")
    settings_env = AppConfig()
    print(f"App Name: {settings_env.app_name}")
    print(f"DB URL: {settings_env.database_url}")

    # Clean up the environment variable for subsequent runs
    del os.environ["APP_NAME"]
    del os.environ["DATABASE_URL"]

Leveraging `.env` Files

from pydantic_settings import BaseSettings, SettingsConfigDict

class ProjectSettings(BaseSettings):
    model_config = SettingsConfigDict(env_file='.env', extra='ignore')

    app_name: str = "Default Project"
    api_key: str = "default_key"

# To make this runnable, you would need python-dotenv installed
# and an actual .env file in the same directory as the script.
# For this lesson, we show the setup.

# Example usage (if .env existed and python-dotenv was active):
# if __name__ == "__main__":
#     settings = ProjectSettings()
#     print(f"App Name: {settings.app_name}")
#     print(f"API Key: {settings.api_key}")

Understanding Settings Priority

Test Your Knowledge!

Recap: Custom Types & Settings