Custom status codes in Flask - Step-by-Step Execution

Concept Flow - Custom status codes

Client sends request

↓

Flask route receives request

↓

Process request logic

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Create response with custom status code

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Send response back to client

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Client receives response with custom status code

The client sends a request, Flask processes it, then returns a response with a custom status code back to the client.

Execution Sample

Flask

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

@app.route('/custom')
def custom_status():
    return jsonify(message='Hello'), 202

This Flask route returns a JSON message with a custom status code 202 (Accepted).

Execution Table

Step	Action	Status Code Set	Response Content	Client Receives
1	Client sends GET /custom	N/A	N/A	Request sent
2	Flask route '/custom' called	N/A	N/A	Waiting for response
3	Return jsonify with message and status 202	202	{"message": "Hello"}	Response received
4	Client processes response	202	{"message": "Hello"}	Message shown with status 202

💡 Response sent with custom status code 202, ending request cycle

Variable Tracker

Variable	Start	After Step 3	Final
status_code	None	202	202
response_content	None	{"message": "Hello"}	{"message": "Hello"}

Key Moments - 2 Insights

Why do we return a tuple with (response, status_code) in Flask?

Flask allows returning a tuple where the second item is the status code. This sets the HTTP status code explicitly, as shown in execution_table step 3.

Can we use any number as a custom status code?

You can use standard HTTP codes or custom ones, but it's best to use valid HTTP status codes. The example uses 202 which means 'Accepted'. See execution_table step 3.

Visual Quiz - 3 Questions

Look at the execution table, what status code is set at step 3?

A 404

B 202

C 200

D 500

💡 Hint

Check the 'Status Code Set' column at step 3 in the execution_table.

At which step does the client receive the response?

A Step 3

B Step 4

C Step 1

D Step 2

💡 Hint

Look at the 'Client Receives' column to find when the response is received.

If we changed the status code to 404, what would change in the execution_table?

A The client would send a different request

B The 'Response Content' would change to an error message

C The 'Status Code Set' at step 3 would be 404

D Nothing would change

💡 Hint

Focus on the 'Status Code Set' column at step 3 in the execution_table.

Concept Snapshot

Flask lets you return a response with a custom status code by returning a tuple: (response, status_code).
Use jsonify() to send JSON data.
Example: return jsonify(message='Hi'), 202
The status code tells the client how to interpret the response.
Common codes: 200 OK, 404 Not Found, 202 Accepted.
Custom codes should follow HTTP standards.

Full Transcript

In Flask, you can send a custom status code by returning a tuple from your route function. The first item is the response data, often created with jsonify for JSON responses. The second item is the status code number, like 202 for Accepted. When a client sends a request, Flask runs the route function, creates the response with the custom status code, and sends it back. The client then receives the response and can act based on the status code. This lets you communicate more precise information about the request result beyond the default 200 OK.