Fast API with Pydentic

FastAPI and Pydantic are often used together to build APIs in Python. FastAPI is a modern, fast (high-performance), web framework for building APIs with Python 3.7+ based on standard Python type hints. Pydantic is a data validation and settings management library that plays well with FastAPI. Here's a simple example:

Let's create an API using FastAPI with Pydantic for request and response models.

```python

from fastapi import FastAPI

from pydantic import BaseModel

app = FastAPI()

# Pydantic model for request

class Item(BaseModel):

    name: str

    description: str = None

    price: float

    quantity: int

# Pydantic model for response

class ItemResponse(BaseModel):

    name: str

    description: str = None

# Endpoint to create an item

@app.post("/items/", response_model=ItemResponse)

async def create_item(item: Item):

    return {"name": item.name, "description": item.description}

# Endpoint to read an item by name

@app.get("/items/{item_name}", response_model=ItemResponse)

async def read_item(item_name: str):

    return {"name": item_name, "description": "Item description"}

# Endpoint to update an item by name

@app.put("/items/{item_name}", response_model=ItemResponse)

async def update_item(item_name: str, item: Item):

    return {"name": item_name, "description": item.description}

```

In this example:

- We define a Pydantic model `Item` for request payload and another `ItemResponse` for the response payload.

- The `create_item` endpoint is for creating an item and expects an `Item` in the request body. It responds with an `ItemResponse`.

- The `read_item` endpoint is for reading an item by name and responds with an `ItemResponse`.

- The `update_item` endpoint is for updating an item by name and expects an `Item` in the request body. It responds with an `ItemResponse`.

FastAPI will automatically generate API documentation (using Swagger UI) based on the type hints and Pydantic models. This is a powerful combination for building robust and well-documented APIs in Python.