Redirects and errors are part of normal web flow.

Redirects

A redirect tells the client: “go to a different URL.”

Common use cases:

• after successful form submission (POST → redirect → GET)
• redirecting legacy URLs

from flask import Flask, redirect, url_for
 
app = Flask(__name__)
 
 
@app.route("/old")
def old():
    return redirect(url_for("new"))
 
 
@app.route("/new")
def new():
    return "New page"

from flask import Flask, redirect, url_for
 
app = Flask(__name__)
 
 
@app.route("/old")
def old():
    return redirect(url_for("new"))
 
 
@app.route("/new")
def new():
    return "New page"

Why redirect after POST?

The PRG pattern (Post/Redirect/Get) prevents form re-submission if the user refreshes.

Errors

You can return an error status code directly:

@app.route("/forbidden")
def forbidden():
    return "No access", 403

@app.route("/forbidden")
def forbidden():
    return "No access", 403

Or use abort()abort():

from flask import abort
 
@app.route("/admin")
def admin():
    abort(403)

from flask import abort
 
@app.route("/admin")
def admin():
    abort(403)

abort()abort() raises an HTTP exception that Flask turns into a proper response.

Common HTTP status codes

• 400 Bad Request — invalid input
• 401 Unauthorized — not logged in (auth missing)
• 403 Forbidden — logged in but not allowed
• 404 Not Found — route/resource doesn’t exist
• 500 Internal Server Error — unhandled exception

🧪 Try It Yourself

Exercise 1 – Create a Flask App

Exercise 2 – Dynamic Route

Exercise 3 – Return JSON