text: from typing import Union
  
  from fastapi import FastAPI
  from fastapi.encoders import jsonable_encoder
  from pydantic import BaseModel
  
  app = FastAPI()
  
  
  class Item(BaseModel):
      name: Union[str, None] = None
      description: Union[str, None] = None
      price: Union[float, None] = None
      tax: float = 10.5
      tags: list[str] = []
  
  
  items = {
      "foo": {"name": "Foo", "price": 50.2},
      "bar": {"name": "Bar", "description": "The bartenders", "price": 62, "tax": 20.2},
      "baz": {"name": "Baz", "description": None, "price": 50.2, "tax": 10.5, "tags": []},
  }
  
  
  @app.get("/items/{item_id}", response_model=Item)
  async def read_item(item_id: str):
      return items[item_id]
  
  
  @app.put("/items/{item_id}", response_model=Item)
  async def update_item(item_id: str, item: Item):
      update_item_encoded = jsonable_encoder(item)
      items[item_id] = update_item_encoded
      return update_item_encoded
  