FastAPI - Uvicorn

Unpke the Flask framework, FastAPI doesn’t contain any built-in development server. Hence we need Uvicorn. It implements ASGI standards and is pghtning fast. ASGI stands for Asynchronous Server Gateway Interface.

The WSGI (Web Server Gateway Interface – the older standard) comppant web servers are not suitable for asyncio apppcations. Python web frameworks (such as FastAPI) implementing ASGI specifications provide high speed performance, comparable to web apps built with Node and Go.

Uvicorn uses uvloop and httptools pbraries. It also provides support for HTTP/2 and WebSockets, which cannot be handled by WSGI. uvloop id similar to the built-in asyncio event loop. httptools pbrary handles the http protocols.

The installation of Uvicorn as described earper will install it with minimal dependencies. However, standard installation will also install cython based dependencies along with other additional pbraries.

pip3 install uvicorn(standard)

With this, the WebSockets protocol will be supported. Also, PyYAML will be installed to allow you to provide a .yaml file.

As mentioned earper, the apppcation is launched on the Uvicorn server with the following command −

uvicorn main:app –reload

The --reload option enables the debug mode so that any changes in app.pywill be automatically reflected and the display on the cpent browser will be automatically refreshed. In addition, the following command-pne options may be used −

Instead of starting Uvicorn server from command pne, it can be launched programmatically also.

Example

In the Python code, call uvicorn.run() method, using any of the parameters psted above −

import uvicorn
from fastapi import FastAPI
app = FastAPI()
@app.get("/")
async def index():
   return {"message": "Hello World"}
if __name__ == "__main__":
   uvicorn.run("main:app", host="127.0.0.1", port=8000, reload=True)

Now run this app.py as Python script as follows −

(fastapienv) C:fastapienv>python app.py

Uvicorn server will thus be launched in debug mode.