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Introduction to Uvicorn, the ASGI server

Introduction to Uvicorn, the ASGI Server​

Uvicorn is a lightning-fast ASGI (Asynchronous Server Gateway Interface) server implementation, running on uvloop and httptools. It serves as the foundation for building your FastAPI applications, providing the asynchronous capabilities that make FastAPI a powerful framework for building web applications. In this tutorial, we will dive into what Uvicorn is, why it's essential for FastAPI, and how to set it up for your FastAPI projects.

What is Uvicorn?​

Uvicorn is a ASGI server that is built to be fast and highly concurrent. It is one of the key components that allow FastAPI to run efficiently and handle multiple requests concurrently due to its asynchronous nature. ASGI, the Asynchronous Server Gateway Interface, is a standard interface between ASGI web applications and servers, much like WSGI is for synchronous Python applications.

Why Uvicorn for FastAPI?​

FastAPI is a modern, fast (high-performance), web framework for building APIs with Python 3.6+ based on standard Python type hints. FastAPI is built to be used with an ASGI server like Uvicorn, providing high performance while also giving the benefits of async and await keywords.

Uvicorn is built on uvloop and httptools. Uvloop is a drop-in replacement for asyncio’s event loop, and it's written in Cython and built on top of libuv, which is a multi-platform support library with a focus on asynchronous I/O operations. This makes Uvicorn an incredibly fast server for Python applications.

Installing Uvicorn​

To install Uvicorn, you can use pip, the Python package installer. Run the following command in your terminal:

pip install uvicorn

This will install Uvicorn and its dependencies, including uvloop and httptools.

Running FastAPI with Uvicorn​

To run your FastAPI application with Uvicorn, you can use the uvicorn command followed by the location of your FastAPI application. For example, if your application is located in a file called main.py, you would run:

uvicorn main:app --reload

Here, main:app refers to the file main.py (main), and the application object app (app). The --reload flag enables hot reloading, which means the server will automatically update whenever you make changes to your code.

Conclusion​

Uvicorn is an essential part of the FastAPI ecosystem, providing a robust, efficient, and asynchronous server to run your FastAPI applications. With its simple installation and usage, it makes setting up a FastAPI environment a breeze. In the next tutorials, we'll delve deeper into FastAPI and how to build powerful APIs with it. Stay tuned!