How to Handle Custom 404 Not Found Responses in FastAPI?

How to Return a Custom 404 Not Found Page Using FastAPI?

When you encounter a 404 response status code, a default error page is usually displayed in web applications. However, you may want to provide a custom 404 page for a more personalized experience. Using FastAPI, implementing a custom 404 page is straightforward.

Custom Exception Handler

An effective method is to leverage a custom exception handler. By specifying the status code you want to handle, you can create a targeted handler.

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

@app.exception_handler(404)
async def not_found_exception_handler(request: Request, exc: HTTPException):
    return RedirectResponse('https://example.com/404')</code>

Exception Handlers Parameter

Alternatively, you can use the exception_handlers parameter of the FastAPI class.

<code class="python">from fastapi import FastAPI, Request

def not_found_error(request: Request, exc: HTTPException):
    return RedirectResponse('https://example.com/404')

exception_handlers = {404: not_found_error}
app = FastAPI(exception_handlers=exception_handlers)</code>

Note: In these examples, a redirect is performed. However, you can return any custom Response, HTMLResponse, or Jinja2 TemplateResponse as needed.

Working Example

Consider the following example:

app.py

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

async def not_found_error(request: Request, exc: HTTPException):
    return RedirectResponse('https://example.com/404')

async def internal_error(request: Request, exc: HTTPException):
    return RedirectResponse('https://example.com/500')

exception_handlers = {404: not_found_error, 500: internal_error}
app = FastAPI(exception_handlers=exception_handlers)</code>

404.html Template

<code class="html">

<title>404 Not Found</title>

<h1 id="Not-Found">Not Found</h1>
<p>The requested resource could not be found.</p>

</code>

500.html Template

<code class="html">

<title>500 Internal Server Error</title>

<h1 id="Internal-Server-Error">Internal Server Error</h1>
<p>An internal error has occurred. Please try again later.</p>

</code>

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