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"><!DOCTYPE html> <html> <title>404 Not Found</title> <body> <h1>Not Found</h1> <p>The requested resource could not be found.</p> </body> </html></code>
500.html Template
<code class="html"><!DOCTYPE html> <html> <title>500 Internal Server Error</title> <body> <h1>Internal Server Error</h1> <p>An internal error has occurred. Please try again later.</p> </body> </html></code>
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