CRUD operations in Flask - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the Flask class from the flask module.

Flask

from flask import [1]
app = Flask(__name__)

Drag options to blanks, or click blank then click option'

AFlask

Bjsonify

Crender_template

DRequest

Attempts:

3 left

💡 Hint

Common Mistakes

Importing Request instead of Flask

Using lowercase flask instead of Flask

The Flask class is imported from the flask module to create the app instance.

2fill in blank

medium

Complete the code to define a route for the home page that returns 'Hello World!'.

Flask

@app.route('/')
def home():
    return [1]

Drag options to blanks, or click blank then click option'

A'Hello World!'

Bjsonify(message='Hello')

Crender_template('index.html')

D'Welcome'

Attempts:

3 left

💡 Hint

Common Mistakes

Returning a function call instead of a string

Forgetting quotes around the string

The route function returns the string 'Hello World!' to display on the home page.

3fill in blank

hard

Fix the error in the code to get JSON data from a POST request.

Flask

from flask import request

@app.route('/data', methods=['POST'])
def data():
    json_data = request.[1]
    return json_data

Drag options to blanks, or click blank then click option'

Ajsonify

Bget_json

Cjson

Ddata

Attempts:

3 left

💡 Hint

Common Mistakes

Calling get_json() on request.json which is not a method

Using jsonify instead of accessing request.json

The request object has a 'json' attribute that holds the parsed JSON data from the request body.

4fill in blank

hard

Fill both blanks to create a route that updates a user by ID using PUT method.

Flask

@app.route('/user/<int:id>', methods=[[1]])
def update_user(id):
    data = request.[2]
    # update logic here
    return 'User updated'

Drag options to blanks, or click blank then click option'

A'PUT'

B'POST'

Cjson

Dform

Attempts:

3 left

💡 Hint

Common Mistakes

Using POST instead of PUT for update

Accessing request.form instead of request.json

The route must accept PUT requests, and the data is accessed from request.json for JSON payload.

5fill in blank

hard

Fill all three blanks to create a route that deletes a user by ID and returns JSON confirmation.

Flask

@app.route('/user/<int:id>', methods=[[1]])
def delete_user(id):
    # delete logic here
    return [2]({'message': 'User deleted', 'id': [3])

Drag options to blanks, or click blank then click option'

A'DELETE'

Bjsonify

Cid

D'GET'

Attempts:

3 left

💡 Hint

Common Mistakes

Using GET instead of DELETE

Returning plain dict instead of jsonify

Not including the id in the response

The route uses DELETE method, returns JSON using jsonify, and includes the user id in the response.

Practice

1. What does the 'CRUD' acronym stand for in Flask web development?

easy

A. Cache, Route, User, Data

B. Connect, Run, Upload, Download

C. Code, Render, Use, Deploy

D. Create, Read, Update, Delete

Solution

1. Step 1: Understand CRUD basics

   CRUD is a common term in web development describing four basic operations on data.

2. Step 2: Match each letter to its meaning

   C stands for Create, R for Read, U for Update, and D for Delete.

3. Final Answer:

   Create, Read, Update, Delete -> Option D

4. Quick Check:

   CRUD = Create, Read, Update, Delete [OK]

Hint: Remember CRUD as the four main data actions [OK]

Common Mistakes:

• Confusing CRUD with unrelated terms
• Mixing up the order of operations
• Thinking CRUD refers to Flask-specific commands

2. Which HTTP method is typically used in Flask to update an existing resource in a CRUD API?

easy

A. PUT

B. POST

C. GET

D. DELETE

Solution

1. Step 1: Identify HTTP methods for CRUD

   GET is for reading, POST for creating, PUT for updating, DELETE for deleting.

2. Step 2: Match update operation

   Updating a resource uses the PUT method in RESTful APIs like Flask.

3. Final Answer:

   PUT -> Option A

4. Quick Check:

   Update = PUT method [OK]

Hint: Update uses PUT method in REST APIs [OK]

Common Mistakes:

• Using POST instead of PUT for updates
• Confusing GET with update actions
• Using DELETE for updating data

3. Given this Flask route code snippet, what will be the output when a DELETE request is sent to /item/5?

from flask import Flask, jsonify
app = Flask(__name__)
items = {1: 'apple', 5: 'banana'}

@app.route('/item/', methods=['DELETE'])
def delete_item(id):
    if id in items:
        del items[id]
        return jsonify({'message': 'Deleted'}), 200
    else:
        return jsonify({'error': 'Not found'}), 404

medium

A. {"error": "Not found"} with status 404

B. {"message": "Deleted"} with status 200

C. SyntaxError due to missing return statement

D. 500 Internal Server Error

Solution

1. Step 1: Check if item with id 5 exists

   The dictionary items contains key 5 with value 'banana'.

2. Step 2: Analyze DELETE request handling

   Since id 5 exists, it is deleted and a JSON message 'Deleted' with status 200 is returned.

3. Final Answer:

   {"message": "Deleted"} with status 200 -> Option B

4. Quick Check:

   Item 5 exists, so deletion returns success message [OK]

Hint: Check if key exists before delete to decide response [OK]

Common Mistakes:

• Assuming item does not exist and returning 404
• Forgetting to delete the item before returning
• Confusing status codes for success and error

4. Identify the error in this Flask route for creating a new item:

@app.route('/item', methods=['POST'])
def create_item():
    data = request.json
    items.append(data['name'])
    return jsonify({'message': 'Item added'}), 201

medium

A. Missing import of request from flask

B. Using append on a dictionary instead of a list

C. Incorrect HTTP method for creating resource

D. Returning wrong status code

Solution

1. Step 1: Check for necessary imports

   The code uses request.json but does not import request from flask.

2. Step 2: Verify data structure usage

   Assuming items is a list, append is valid; HTTP method POST is correct; status 201 is correct.

3. Final Answer:

   Missing import of request from flask -> Option A

4. Quick Check:

   request must be imported to access request.json [OK]

Hint: Always import request to access JSON data in Flask [OK]

Common Mistakes:

• Forgetting to import request
• Using append on a dict instead of list
• Using GET instead of POST for creation

5. You want to implement a Flask route to update an item only if it exists, otherwise return a 404 error. Which code snippet correctly performs this update using JSON data sent in a PUT request? A)

@app.route('/item/', methods=['PUT'])
def update_item(id):
    data = request.json
    items[id] = data['name']
    return jsonify({'message': 'Updated'}), 200

B)

@app.route('/item/', methods=['PUT'])
def update_item(id):
    if id not in items:
        return jsonify({'error': 'Not found'}), 404
    data = request.json
    items[id] = data['name']
    return jsonify({'message': 'Updated'}), 200

C)

@app.route('/item/', methods=['POST'])
def update_item(id):
    data = request.json
    if id in items:
        items[id] = data['name']
    return jsonify({'message': 'Updated'}), 200

D)

@app.route('/item/', methods=['PUT'])
def update_item(id):
    data = request.json
    if id in items:
        items[id] = data['name']
    else:
        items[id] = 'default'
    return jsonify({'message': 'Updated'}), 200

hard

A. Updates without checking existence, always returns 200

B. Uses POST method incorrectly for update

C. Checks existence, updates if found, else returns 404

D. Adds default if not found instead of 404 error

Solution

1. Step 1: Verify HTTP method and existence check

   Checks existence, updates if found, else returns 404 uses PUT method and checks if id exists before updating.

2. Step 2: Confirm correct response for missing item

   If id not found, it returns 404 error, which is correct behavior for update.

3. Final Answer:

   Checks existence, updates if found, else returns 404 -> Option C

4. Quick Check:

   Update with existence check returns 404 if missing [OK]

Hint: Always check if item exists before update to avoid errors [OK]

Common Mistakes:

• Not checking if item exists before update
• Using POST instead of PUT for update
• Adding default values instead of error on missing item