Redirect and abort functions in Flask - Step-by-Step Execution

Concept Flow - Redirect and abort functions

Start Request

↓

Check Condition

↓

Call abort

↓

Send Error

↓

End Request

When a request comes in, Flask checks a condition. If something is wrong, it aborts with an error. Otherwise, it redirects the user to another page.

Execution Sample

Flask

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

@app.route('/secret')
def secret():
    abort(403)

@app.route('/go-home')
def go_home():
    return redirect('/')

This code aborts with a 403 error on '/secret' and redirects to '/' on '/go-home'.

Execution Table

Step	Request URL	Condition	Function Called	Response Sent
1	/secret	Always abort	abort(403)	403 Forbidden Error
2	/go-home	Always redirect	redirect('/')	302 Redirect to '/'
3	/other	No abort or redirect	None	Normal response or 404

💡 Execution stops after sending error or redirect response to client.

Variable Tracker

Variable	Start	After /secret	After /go-home	After /other
Request URL	None	/secret	/go-home	/other
Condition	None	True (abort)	False (redirect)	False (normal)
Function Called	None	abort(403)	redirect('/')	None
Response Sent	None	403 Error	302 Redirect	Normal or 404

Key Moments - 3 Insights

Why does abort stop the request immediately?

Because abort raises an exception that Flask catches to send an error response right away, as shown in step 1 of the execution_table.

What happens after redirect is called?

Redirect sends a 302 response telling the browser to go to a new URL, ending the current request, as seen in step 2 of the execution_table.

Can both abort and redirect happen in the same request?

No, only one response is sent per request. The first function called that sends a response ends the request, shown by the exclusive branches in the concept_flow.

Visual Quiz - 3 Questions

Look at the execution_table, what response is sent when the URL is '/secret'?

A 302 Redirect to '/'

B 403 Forbidden Error

C 200 OK Normal Response

D 404 Not Found

💡 Hint

Check the row where Request URL is '/secret' in the execution_table.

At which step does Flask send a redirect response?

A Step 1

B Step 3

C Step 2

D No redirect sent

💡 Hint

Look for 'redirect' in the Function Called column in the execution_table.

If the condition for abort changes to False on '/secret', what will happen?

A Normal response or 404 will be sent

B Redirect will be called instead

C Abort still sends 403 error

D Both abort and redirect will run

💡 Hint

Refer to the Condition and Response Sent columns in the variable_tracker for '/other' as a similar case.

Concept Snapshot

Flask redirect and abort:
- Use abort(code) to stop and send an error (e.g., 403).
- Use redirect(url) to send a 302 redirect response.
- Only one response per request is sent.
- abort raises an exception; redirect returns a response.
- Both help control user flow and error handling.

Full Transcript

In Flask, when a request comes in, the app checks conditions. If something is wrong, abort is called to stop the request and send an error code like 403. If redirect is needed, Flask sends a 302 response telling the browser to go to another URL. Only one of these functions runs per request. The execution table shows how different URLs trigger abort or redirect and what responses are sent. Variables track the request URL, condition, function called, and response sent. Key moments clarify why abort stops immediately and how redirect works. The quiz tests understanding of these steps. This helps beginners see how Flask controls request flow with redirect and abort.