[Solved] You want to use before_request in Flask to verify if a user is authenticated by checking session['user_id']. If not authenticated, redirect to /login. Which snippet correctly implements this? | Flask

Flask - Middleware and Extensions

You want to use before_request in Flask to verify if a user is authenticated by checking session['user_id']. If not authenticated, redirect to /login. Which snippet correctly implements this?

A

<pre>from flask import Flask, session, redirect, url_for
app = Flask(__name__)

@app.before_request
def check_login():
    if 'user_id' not in session:
        return redirect(url_for('login'))</pre>

B

<pre>@app.before_request()
def check_login():
    if session['user_id'] is None:
        redirect('/login')</pre>

C

<pre>@app.before_request
def check_login():
    if session.get('user_id'):
        return redirect('/login')</pre>

D

<pre>@app.before_request
def check_login():
    if 'user_id' in session:
        pass
    else:
        abort(401)</pre>

Step-by-Step Solution

Solution:

Step 1: Check decorator syntax

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

@app.before_request
def check_login():
    if 'user_id' not in session:
        return redirect(url_for('login'))

correctly uses @app.before_request without parentheses.

Step 2: Verify session check and redirect

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

@app.before_request
def check_login():
    if 'user_id' not in session:
        return redirect(url_for('login'))

checks if 'user_id' is missing and returns a redirect response properly.

Step 3: Analyze other options

@app.before_request()
def check_login():
    if session['user_id'] is None:
        redirect('/login')

uses parentheses incorrectly and does not return redirect.

@app.before_request
def check_login():
    if session.get('user_id'):
        return redirect('/login')

redirects if user_id exists, which is wrong logic.

@app.before_request
def check_login():
    if 'user_id' in session:
        pass
    else:
        abort(401)

aborts with 401 instead of redirecting.

Final Answer:
Option A -> Option A
Quick Check:
Return redirect to stop request processing. [OK]

Quick Trick: Return redirect in before_request to halt and redirect [OK]

Common Mistakes:

MISTAKES

Using parentheses in decorator
Not returning redirect response
Incorrect logic for authentication check
Using abort instead of redirect

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More Flask Quizzes

You want to use before_request in Flask to verify if a user is authenticated by checking session['user_id']. If not authenticated, redirect to /login. Which snippet correctly implements this?

Step 1: Check decorator syntax

Step 2: Verify session check and redirect

Step 3: Analyze other options

Final Answer:

Quick Check:

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