# Simple API with FastAPI

This guide demonstrates how to build a high-performance API using **FastAPI**. FastAPI is a modern, fast (high-performance), web framework for building APIs with Python 3.8+ based on standard Python type hints.

**Modules Used:**
*   `fastapi`: The web framework.
*   `uvicorn`: An ASGI web server implementation for Python.
*   `pydantic`: For data validation and settings management using Python type annotations.

## Installation

```bash
pip install fastapi uvicorn
```

## The Code

Save this as `main.py`.

```python
from fastapi import FastAPI, HTTPException
from pydantic import BaseModel
from typing import List, Optional

app = FastAPI()

# --- Data Model ---
class Item(BaseModel):
    id: int
    name: str
    price: float
    is_offer: Optional[bool] = None

# --- In-Memory Database ---
items_db = []

# --- Endpoints ---

@app.get("/")
def read_root():
    return {"Hello": "World"}

@app.get("/items/", response_model=List[Item])
def read_items():
    return items_db

@app.get("/items/{item_id}", response_model=Item)
def read_item(item_id: int):
    for item in items_db:
        if item.id == item_id:
            return item
    raise HTTPException(status_code=404, detail="Item not found")

@app.post("/items/", response_model=Item)
def create_item(item: Item):
    # Check if ID already exists
    for existing_item in items_db:
        if existing_item.id == item.id:
            raise HTTPException(status_code=400, detail="Item ID already exists")
    
    items_db.append(item)
    return item

@app.put("/items/{item_id}", response_model=Item)
def update_item(item_id: int, item: Item):
    for index, existing_item in enumerate(items_db):
        if existing_item.id == item_id:
            # Update the item
            items_db[index] = item
            return item
    raise HTTPException(status_code=404, detail="Item not found")

@app.delete("/items/{item_id}")
def delete_item(item_id: int):
    for index, item in enumerate(items_db):
        if item.id == item_id:
            del items_db[index]
            return {"message": "Item deleted"}
    raise HTTPException(status_code=404, detail="Item not found")

# To run programmatically (optional, usually run via CLI)
if __name__ == "__main__":
    import uvicorn
    uvicorn.run(app, host="127.0.0.1", port=8000)
```

## Usage

1.  **Run the server:**
    You can run it using the `uvicorn` command line tool (recommended for development with auto-reload):
    ```bash
    uvicorn main:app --reload
    ```

2.  **Interactive Documentation (Swagger UI):**
    FastAPI automatically generates interactive API documentation.
    Go to `http://127.0.0.1:8000/docs`.
    Here you can test all your endpoints (GET, POST, PUT, DELETE) directly from the browser.

[[programming/python/python]]