- Request Body(Not Necessarily) : send data from a Client(a browser) → API - Response Body(Necessarily) : data from API → a Client(a browser) Step 1. Declare a request body using Pydantic. from pydantic import BaseModel 2. Declare the data model as a class that inherits from BaseModel. class Item(BaseModel): name: str description: Union[str, None] = None price: float tax: Union[float, None] = No..