Redirect and abort functions in Flask - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the redirect() function do in Flask?

The redirect() function sends the user to a different URL. It tells the browser to load a new page, like when you click a link.

beginner

How do you use the abort() function in Flask?

You call abort() with an HTTP status code (like 404) to stop the request and show an error page. It’s like saying "Stop! This page is not found."

intermediate

What HTTP status code does redirect() usually use by default?

By default, redirect() uses status code 302, which means "Found" or "Temporary Redirect." It tells the browser to go to the new URL temporarily.

beginner

What happens if you call abort(404) in a Flask route?

Flask stops running the route and sends a 404 Not Found error page to the user. This means the page does not exist.

intermediate

Can you customize the error page shown by abort() in Flask?

Yes! You can create custom error handlers for codes like 404 or 500 to show friendly messages or pages instead of the default error page.

What does redirect('/home') do in a Flask app?

A Reloads the current page

B Stops the app with an error

C Sends the user to the '/home' URL

D Deletes the '/home' route

redirect('/home') tells the browser to go to the '/home' page.

Which function stops a Flask route and shows an error page?

A abort()

B redirect()

C render_template()

D url_for()

abort() stops the route and sends an error response.

What HTTP status code is commonly used by abort(404)?

A 200

B 404

C 302

D 500

abort(404) sends a 404 Not Found error.

Which status code does redirect() use by default?

A 302

B 500

C 404

D 301

Default redirect status code is 302 (Temporary Redirect).

How can you show a custom error page for abort(404) in Flask?

A Change the route URL

B Use <code>redirect()</code>

C Call <code>abort()</code> again

D Create an error handler for 404

Custom error handlers let you show friendly pages for errors.

Explain how and why you would use the redirect() function in a Flask app.

Think about when you want to send someone to a different page after an action.

Describe the purpose of the abort() function and how it affects the user experience in Flask.

Consider what happens when a page is not found or access is denied.

Practice

1. What does the redirect function do in a Flask application?

easy

A. Sends the user to a different URL

B. Stops the request and shows an error code

C. Returns a JSON response

D. Renders an HTML template

Solution

1. Step 1: Understand the purpose of redirect

   The redirect function is used to send the user to a different URL in the browser.

2. Step 2: Compare with other functions

   Unlike abort which stops the request with an error, redirect changes the page location.

3. Final Answer:

   Sends the user to a different URL -> Option A

4. Quick Check:

   redirect = Send user to new URL [OK]

Hint: Redirect sends users to new pages, abort shows errors [OK]

Common Mistakes:

• Confusing redirect with abort
• Thinking redirect stops the request
• Assuming redirect returns HTML directly

2. Which of the following is the correct way to import and use abort in Flask?

easy

A. import flask.abort; abort(404)

B. import abort from flask; abort(404)

C. from flask import abort; abort['404']

D. from flask import abort; abort(404)

Solution

1. Step 1: Check correct import syntax

   In Flask, functions like abort are imported using from flask import abort.

2. Step 2: Check correct usage

   The abort function is called with parentheses and an integer status code, e.g., abort(404).

3. Final Answer:

   from flask import abort; abort(404) -> Option D

4. Quick Check:

   Correct import and call syntax = from flask import abort; abort(404) [OK]

Hint: Use 'from flask import abort' and call abort(code) [OK]

Common Mistakes:

• Using wrong import syntax
• Calling abort with brackets instead of parentheses
• Trying to import abort with 'import abort from flask'

3. What will be the output when this Flask route is accessed?

from flask import Flask, redirect
app = Flask(__name__)

@app.route('/')
def home():
    return redirect('/welcome')

@app.route('/welcome')
def welcome():
    return 'Hello, welcome!'

medium

A. Shows a 404 error

B. Displays 'Hello, welcome!' in the browser

C. Returns a JSON response with 'Hello, welcome!'

D. Causes a server crash

Solution

1. Step 1: Analyze the '/' route

   The '/' route calls redirect('/welcome'), sending the browser to '/welcome'.

2. Step 2: Analyze the '/welcome' route

   The '/welcome' route returns the string 'Hello, welcome!'. So the browser shows this text.

3. Final Answer:

   Displays 'Hello, welcome!' in the browser -> Option B

4. Quick Check:

   Redirect leads to '/welcome' which returns greeting [OK]

Hint: Redirect sends user to new route which returns the message [OK]

Common Mistakes:

• Thinking redirect returns text directly
• Expecting JSON instead of plain text
• Assuming redirect causes error or crash

4. Identify the error in this Flask code snippet:

from flask import Flask, abort
app = Flask(__name__)

@app.route('/secret')
def secret():
    abort(403)
    return 'You should not see this'

medium

A. The return statement after abort is unreachable

B. abort must be called with a string, not a number

C. abort cannot be used inside route functions

D. Missing parentheses in abort call

Solution

1. Step 1: Understand abort behavior

   The abort(403) immediately stops the request and sends a 403 error response.

2. Step 2: Check code after abort

   The return statement after abort is never reached, so it is unreachable code.

3. Final Answer:

   The return statement after abort is unreachable -> Option A

4. Quick Check:

   Code after abort is ignored [OK]

Hint: Code after abort() won't run; it's unreachable [OK]

Common Mistakes:

• Thinking abort needs string argument
• Believing abort can't be used in routes
• Forgetting abort stops execution immediately

5. You want to redirect users to a login page if they are not authenticated, otherwise show their dashboard. Which Flask code snippet correctly uses redirect and abort to handle this?

hard

A. if not user_authenticated:
abort(401)
else:
return redirect('/dashboard')

B. if user_authenticated:
return redirect('/login')
else:
abort(200)

C. if not user_authenticated:
return redirect('/login')
else:
return 'Welcome to your dashboard!'

D. if user_authenticated:
abort(404)
else:
return redirect('/login')

Solution

1. Step 1: Understand user authentication logic

   If the user is not authenticated, they should be sent to the login page using redirect('/login').

2. Step 2: Handle authenticated users

   If authenticated, show the dashboard message directly with a return string.

3. Step 3: Check abort usage

   Using abort for normal redirects or success codes is incorrect; abort is for errors.

4. Final Answer:

   if not user_authenticated: return redirect('/login') else: return 'Welcome to your dashboard!' -> Option C

5. Quick Check:

   Redirect unauthenticated, show dashboard if authenticated [OK]

Hint: Redirect unauthenticated users, return dashboard text if authenticated [OK]

Common Mistakes:

• Using abort for normal redirects
• Aborting with success codes like 200
• Redirecting authenticated users to login