How Flask processes HTTP requests - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import Flask and create an app instance.

Flask

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

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

Arender_template

BFlask

CRequest

Dredirect

Attempts:

3 left

💡 Hint

Common Mistakes

Importing Request instead of Flask

Forgetting to create the app instance

Flask is imported from the flask package and used to create the app instance.

2fill in blank

medium

Complete the code to define a route for the home page.

Flask

@app.route('[1]')
def home():
    return 'Hello, Flask!'

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

A/

B/home

C/index.html

D/main

Attempts:

3 left

💡 Hint

Common Mistakes

Using '/home' instead of '/' for the root route

Forgetting the leading slash

The root URL '/' is used to define the home page route in Flask.

3fill in blank

hard

Fix the error in the code to run the Flask app only when the script is executed directly.

Flask

if __name__ == [1]:
    app.run(debug=True)

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

A'__main__'

B'run'

C'app'

D'main'

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'main' without underscores

Using 'app' or 'run' instead of '__main__'

The special variable __name__ equals '__main__' when the script is run directly.

4fill in blank

hard

Fill both blanks to access the HTTP method and return it in the response.

Flask

from flask import request

@app.route('/method', methods=['GET', 'POST'])
def method():
    method_used = request.[1]
    return f'Method used: [2]'

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

Amethod

Bmethod_used

Cmethod()

Dmethod_used()

Attempts:

3 left

💡 Hint

Common Mistakes

Using request.method() as if it were a function

Returning request.method directly without storing

request.method gives the HTTP method as a string. We store it in method_used and return it.

5fill in blank

hard

Fill all three blanks to extract a URL parameter and return a greeting.

Flask

@app.route('/hello/<[1]>')
def hello([2]):
    return f'Hello, [3]!'

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

Aname

Busername

Duser

Attempts:

3 left

💡 Hint

Common Mistakes

Mismatching parameter name and function argument

Using different variable names in the return string

The URL parameter is named 'name'. The function argument must match it. The greeting uses that variable.

Practice

1. What does Flask use to decide which function should handle an incoming HTTP request?

easy

A. The route URL pattern defined with @app.route

B. The order in which functions are defined in the code

C. The size of the HTTP request body

D. The IP address of the client

Solution

1. Step 1: Understand Flask routing

   Flask uses route decorators like @app.route to map URLs to functions.

2. Step 2: Match incoming request URL

   When a request comes, Flask matches its URL to the route patterns to find the right function.

3. Final Answer:

   The route URL pattern defined with @app.route -> Option A

4. Quick Check:

   Routing = @app.route [OK]

Hint: Routes connect URLs to functions in Flask [OK]

Common Mistakes:

• Thinking function order matters
• Confusing client IP with routing
• Using request size to route

2. Which of the following is the correct way to define a Flask route that only accepts POST requests?

easy

A. @app.route('/submit', methods=['GET'])

B. @app.route('/submit', accept='POST')

C. @app.route('/submit', methods=['POST'])

D. @app.route('/submit', method='POST')

Solution

1. Step 1: Check correct syntax for methods argument

   Flask route decorator uses methods=['POST'] to specify allowed HTTP methods.

2. Step 2: Identify the correct option

   @app.route('/submit', methods=['POST']) uses methods=['POST'], which is the correct syntax.

3. Final Answer:

   @app.route('/submit', methods=['POST']) -> Option C

4. Quick Check:

   methods=['POST'] sets POST only [OK]

Hint: Use methods=['POST'] to allow only POST requests [OK]

Common Mistakes:

• Using method instead of methods
• Using accept instead of methods
• Allowing GET instead of POST

3. Given this Flask code snippet:

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

@app.route('/greet', methods=['POST'])
def greet():
    name = request.form.get('name', 'Guest')
    return f'Hello, {name}!'

What will be the response if a POST request is sent to '/greet' with form data name='Alice'?

medium

A. Hello, Guest!

B. Hello, Alice!

C. Hello, None!

D. Error: Missing name parameter

Solution

1. Step 1: Understand request.form.get usage

   The code tries to get 'name' from form data; if missing, defaults to 'Guest'.

2. Step 2: Analyze the POST request data

   The POST request includes name='Alice', so request.form.get('name') returns 'Alice'.

3. Final Answer:

   Hello, Alice! -> Option B

4. Quick Check:

   Form data name='Alice' returns 'Hello, Alice!' [OK]

Hint: request.form.get returns form value or default [OK]

Common Mistakes:

• Assuming default 'Guest' always used
• Confusing GET and POST data
• Expecting error if parameter missing

4. What is wrong with this Flask route code?

@app.route('/data', methods=['GET', 'POST'])
def data():
    if request.method == 'POST'
        return 'Posted data'
    else:
        return 'Get data'

medium

A. Missing colon after if statement

B. request.method is not valid in Flask

C. Route decorator should not have methods argument

D. Function name cannot be 'data'

Solution

1. Step 1: Check syntax of if statement

   The if statement lacks a colon at the end, causing a syntax error.

2. Step 2: Verify other parts

   request.method is valid, methods argument is correct, function name is allowed.

3. Final Answer:

   Missing colon after if statement -> Option A

4. Quick Check:

   if statement needs colon [OK]

Hint: Check colons after if/else statements [OK]

Common Mistakes:

• Forgetting colon after if
• Thinking request.method is invalid
• Misunderstanding methods argument

5. You want to create a Flask route '/submit' that accepts both GET and POST requests. When accessed by GET, it should show a form. When accessed by POST, it should process form data and return a confirmation message. Which code snippet correctly implements this behavior?

hard

A. from flask import Flask, request
app = Flask(__name__)

@app.route('/submit', methods=['GET', 'POST'])
def submit():
return 'Submit page'

B. from flask import Flask, request
app = Flask(__name__)

@app.route('/submit')
def submit():
if request.method == 'POST':
return 'Data received'
else:
return ''

C. from flask import Flask
app = Flask(__name__)

@app.route('/submit', methods=['POST'])
def submit():
return 'Only POST allowed'

D. from flask import Flask, request
app = Flask(__name__)

@app.route('/submit', methods=['GET', 'POST'])
def submit():
if request.method == 'POST':
data = request.form.get('data')
return f'Data received: {data}'
else:
return ''''''

Solution

1. Step 1: Check methods argument

   from flask import Flask, request app = Flask(__name__) @app.route('/submit', methods=['GET', 'POST']) def submit(): if request.method == 'POST': data = request.form.get('data') return f'Data received: {data}' else: return '''''' correctly uses methods=['GET', 'POST'] to accept both request types.

2. Step 2: Verify request method handling

   from flask import Flask, request app = Flask(__name__) @app.route('/submit', methods=['GET', 'POST']) def submit(): if request.method == 'POST': data = request.form.get('data') return f'Data received: {data}' else: return '''''' checks request.method and returns form HTML for GET and processes form data for POST.

3. Step 3: Compare other options

   The other options either miss methods argument, do not handle both methods properly, or do not return form on GET.

4. Final Answer:

   The code snippet that uses methods=['GET', 'POST'], checks request.method, returns form for GET and processes data for POST -> Option D

5. Quick Check:

   methods=['GET','POST'] + if request.method [OK]

Hint: Use methods=['GET','POST'] and check request.method [OK]

Common Mistakes:

• Not specifying methods argument
• Not checking request.method
• Returning same response for all methods