Flask route as API endpoint - Mini Project: Build & Apply

Flask route as API endpoint

📖 Scenario: You are building a simple web service that provides information about fruits. This service will have an API endpoint that returns fruit data in JSON format.

🎯 Goal: Create a Flask application with a route /api/fruits that returns a JSON response containing a list of fruits and their colors.

📋 What You'll Learn

Create a dictionary called fruits with fruit names as keys and their colors as values

Create a Flask app instance named app

Define a route /api/fruits using the @app.route decorator

Return the fruits dictionary as a JSON response using jsonify

💡 Why This Matters

🌍 Real World

APIs like this let apps and websites get data from servers in a simple, standard way.

💼 Career

Knowing how to create API endpoints with Flask is useful for backend web development jobs.

1

Create the fruit data dictionary

Create a dictionary called fruits with these exact entries: 'apple': 'red', 'banana': 'yellow', and 'grape': 'purple'.

Flask

# Your code here

Hint

Use curly braces {} to create a dictionary with keys and values.

2

Create the Flask app instance

Import Flask from flask and create a Flask app instance called app.

Flask

fruits = {'apple': 'red', 'banana': 'yellow', 'grape': 'purple'}
# Your code here

Hint

Use app = Flask(__name__) to create the app instance.

3

Define the API route

Use the @app.route decorator with the path /api/fruits to define a function called get_fruits.

Flask

from flask import Flask

fruits = {'apple': 'red', 'banana': 'yellow', 'grape': 'purple'}

app = Flask(__name__)

# Your code here

Hint

Use @app.route('/api/fruits') above the function definition.

4

Return JSON response with fruit data

Import jsonify from flask and return jsonify(fruits) inside the get_fruits function.

Flask

from flask import Flask

fruits = {'apple': 'red', 'banana': 'yellow', 'grape': 'purple'}

app = Flask(__name__)

@app.route('/api/fruits')
def get_fruits():
    # Your code here

Hint

Use return jsonify(fruits) to send the dictionary as JSON.

Practice

1. What does a Flask route do in a web application?

easy

A. It styles the webpage with CSS.

B. It stores data in a database automatically.

C. It compiles Python code into machine code.

D. It defines a URL where the app listens for requests.

Solution

1. Step 1: Understand the role of a route

   A Flask route sets a specific web address that the app listens to for incoming requests.

2. Step 2: Identify what routes do not do

   Routes do not handle styling, database storage automatically, or code compilation.

3. Final Answer:

   It defines a URL where the app listens for requests. -> Option D

4. Quick Check:

   Flask route = URL listener [OK]

Hint: Routes map URLs to functions handling requests [OK]

Common Mistakes:

• Thinking routes handle styling or database storage
• Confusing routes with frontend design
• Assuming routes compile code

2. Which of the following is the correct syntax to create a Flask route for the URL '/api/data'?

easy

A. @app.route('/api/data')\ndef get_data():\n return 'data'

B. @app.route('/api/data')\nfunction get_data() { return 'data'; }

C. app.route('/api/data')\ndef get_data():\n return 'data'

D. @app.route('/api/data')\ndef get_data():\nprint('data')

Solution

1. Step 1: Check Flask route decorator syntax

   The correct syntax uses @app.route('/api/data') above a Python function definition.

2. Step 2: Verify function and return statement

   The function must be defined with def and return a value; print does not send a response.

3. Final Answer:

   @app.route('/api/data')\ndef get_data():\n return 'data' -> Option A

4. Quick Check:

   Python route decorator + def + return = D [OK]

Hint: Use @app.route decorator and def function with return [OK]

Common Mistakes:

• Using JavaScript syntax inside Flask route
• Missing @ before app.route
• Using print instead of return in route function

3. What will be the output when accessing the '/hello' route in this Flask app?

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

@app.route('/hello')
def hello():
    return jsonify({'message': 'Hello, world!'})

medium

A. {'message': 'Hello, world!'} as JSON response

B. Plain text: Hello, world!

C. HTML page with 'Hello, world!' text

D. Error: jsonify is not defined

Solution

1. Step 1: Understand jsonify usage

   The function returns jsonify({'message': 'Hello, world!'}), which sends a JSON response.

2. Step 2: Identify response type

   The response is JSON formatted, not plain text or HTML, and no error occurs because jsonify is imported.

3. Final Answer:

   {'message': 'Hello, world!'} as JSON response -> Option A

4. Quick Check:

   jsonify returns JSON response [OK]

Hint: jsonify returns JSON, not plain text or HTML [OK]

Common Mistakes:

• Confusing jsonify with print or return string
• Expecting HTML instead of JSON
• Forgetting to import jsonify

4. Identify the error in this Flask route code:

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

@app.route('/data')
def data():
    return json({'key': 'value'})

medium

A. Missing @ before app.route decorator

B. json is not imported or defined; should use jsonify

C. Function name 'data' is invalid

D. Route URL must start with '/api/'

Solution

1. Step 1: Check function return statement

   The code uses json({'key': 'value'}) but json is not imported or defined.

2. Step 2: Identify correct function for JSON response

   Flask provides jsonify to return JSON responses, which is imported here.

3. Final Answer:

   json is not imported or defined; should use jsonify -> Option B

4. Quick Check:

   Use jsonify, not json, for JSON response [OK]

Hint: Use jsonify, not json, to return JSON in Flask [OK]

Common Mistakes:

• Using json instead of jsonify
• Forgetting to import jsonify
• Assuming function names must follow special rules

5. You want to create a Flask API endpoint '/user/' that returns JSON with the user's id and a greeting message. Which code correctly implements this?

hard

A. @app.route('/user/')\ndef user():\n return jsonify({'id': id, 'message': 'Hello user'})

B. @app.route('/user/<id>')\ndef user(id):\n return {'id': id, 'message': 'Hello user ' + id}

C. @app.route('/user/')\ndef user(id):\n return jsonify({'id': id, 'message': f'Hello user {id}'})

D. @app.route('/user/')\ndef user(id):\n print({'id': id, 'message': f'Hello user {id}'})

Solution

1. Step 1: Check route URL and parameter type

   The route uses '/user/' which correctly captures an integer parameter named id.

2. Step 2: Verify function parameters and return

   The function accepts id and returns a JSON response using jsonify with the correct message format.

3. Step 3: Identify errors in other options

   @app.route('/user/<id>')\ndef user(id):\n return {'id': id, 'message': 'Hello user ' + id} misses int type and returns a dict without jsonify; @app.route('/user/')\ndef user():\n return jsonify({'id': id, 'message': 'Hello user'}) misses id parameter; @app.route('/user/')\ndef user(id):\n print({'id': id, 'message': f'Hello user {id}'}) uses print instead of return.

4. Final Answer:

   @app.route('/user/')\ndef user(id):\n return jsonify({'id': id, 'message': f'Hello user {id}'}) -> Option C

5. Quick Check:

   Route with int param + jsonify return = A [OK]

Hint: Use in route and return jsonify with id [OK]

Common Mistakes:

• Not specifying for integer parameter
• Returning dict without jsonify
• Using print instead of return in route