Example

1. Create

Create a file main.py with:

from typing import Optional

from fastapi import FastAPI


app = FastAPI()


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


@app.get("/items/{item_id}")
def read_item(item_id: int, q: Optional[str] = None):
    return {"item_id": item_id, "q": q}

2. Run

Run the server with:

$ pipenv run uvicorn main:app --reload
INFO:     Uvicorn running on http://127.0.0.1:8000 (Press CTRL+C to quit)
INFO:     Started reloader process [89155] using statreload
INFO:     Started server process [89164]
INFO:     Waiting for application startup.
INFO:     Application startup complete.

3. Check

Open your browser at http://127.0.0.1:8000/ and you will see:

You will also get an interactive API documentation provided by Swagger UI at http://127.0.0.1:8000/docs:

You will also get an alternative automatic documentation provided by ReDoc at http://127.0.0.1:8000/redoc:

4. Update

Now we modify the file main.py to receive a body from a PUT request:

 from typing import Optional

 from pydantic import BaseModel

 from fastapi import FastAPI


 app = FastAPI()


 class Item(BaseModel):
     name: str
     price: float
     is_offer: Optional[bool] = None


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


 @app.get("/items/{item_id}")
 def read_item(item_id: int, q: Optional[str] = None):
     return {"item_id": item_id, "q": q}


 @app.put("/items/{item_id}")
 def update_item(item_id: int, item: Item):
     return {"item_name": item.name, "item_id": item_id}

The server should reload the file automatically because we added --reload to the uvicorn command. Also the interactive API documentation will show the new body with PUT. If you click on the button Try it out you will fill in the parameter for item_id. Then click on the Execute button and the your browser will send the parameter to the API and show them on the screen, for example as response body:

{
  "item_name": "string",
  "item_id": 1234
}