How to Handle 404 Responses with Custom Pages in FastAPI?

Handling 404 Responses with Custom Pages in FastAPI

Introduction

FastAPI is a popular web framework for Python that provides a clean and efficient way to build APIs. One common requirement when working with web applications is the ability to customize the response returned when a requested resource is not found (404 Not Found). This article will guide you through the process of creating a custom 404 page using FastAPI.

Using a Custom Response Handler

One approach to handle 404 responses is to use a custom exception handler. FastAPI allows you to register custom exception handlers that can intercept and handle specific exceptions. In our case, we can create an exception handler for the 404 status code and return a custom response.

Here's an example of how to create a custom 404 response handler:

<code class="python">from fastapi.exceptions import HTTPException
from fastapi.responses import HTMLResponse

@app.exception_handler(404)
async def not_found_handler(request: Request, exc: HTTPException):
    return HTMLResponse("<h1>Not Found</h1><p>The requested resource could not be found.</p>", status_code=404)</code>

Using a Middleware

Another option for handling 404 responses is to use a middleware. Middlewares are functions that run before and after each request-response cycle. In our case, we can use a middleware to check for 404 responses and return a custom response.

Here's an example of how to create a middleware to handle 404 responses:

<code class="python">from fastapi import Request, Response, status
from fastapi.responses import HTMLResponse

@app.middleware(&quot;http&quot;)
async def handle_404(request: Request, call_next):
    response = await call_next(request)
    if response.status_code == status.HTTP_404_NOT_FOUND:
        return HTMLResponse("<h1>Not Found</h1><p>The requested resource could not be found.</p>")
    return response</code>

Note: It is important to note that if you are using both a custom response handler and a middleware to handle 404 responses, the middleware will take precedence.

Conclusion

Customizing 404 responses in FastAPI is a straightforward process that can be achieved using either custom response handlers or middleware. By following the techniques described in this article, you can create custom 404 pages that provide a more informative and user-friendly experience.

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