Request object properties in Flask - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the Flask request object used for?

The request object in Flask holds all the information about the current HTTP request, like form data, query parameters, headers, and more.

beginner

How do you access form data sent via POST in Flask?

Use request.form to get form data sent in a POST request. It acts like a dictionary with form field names as keys.

beginner

What property of request gives you URL query parameters?

request.args contains the URL query parameters as a dictionary-like object.

beginner

How can you get the HTTP method (GET, POST, etc.) of the current request?

Use request.method to find out the HTTP method used for the request.

intermediate

What property would you use to access JSON data sent in a request?

Use request.get_json() to get JSON data sent in the request body. It returns a Python dictionary if JSON is valid.

Which request property holds form data sent via POST?

A request.args

B request.json

C request.data

D request.form

request.form contains form data sent in POST requests.

How do you get the HTTP method of the current request in Flask?

A request.type

B request.method

C request.action

D request.mode

request.method returns the HTTP method like GET or POST.

Which property contains URL query parameters?

A request.args

B request.form

C request.query

D request.params

request.args holds the URL query parameters.

To access JSON data sent in a request body, you use:

A request.body

B request.data

C request.json

D request.form

request.json parses JSON data from the request body.

Which request property gives you access to raw request data?

A request.data

B request.args

C request.form

D request.json

request.data contains the raw request body as bytes.

Explain how to access form data, query parameters, and JSON data from a Flask request object.

Think about where each type of data is sent in an HTTP request.

Describe how to determine the HTTP method of a request in Flask and why it might be useful.

Consider how web forms and APIs behave differently with GET and POST.

Practice

1. What does request.method in Flask represent?

easy

A. The client's IP address

B. The URL path requested by the client

C. The response status code

D. The HTTP method used by the client (GET, POST, etc.)

Solution

1. Step 1: Understand the role of request.method

   This property tells you which HTTP method the client used to send the request, such as GET or POST.

2. Step 2: Differentiate from other request properties

   It is not the URL path, IP address, or response code, which are accessed differently.

3. Final Answer:

   The HTTP method used by the client (GET, POST, etc.) -> Option D

4. Quick Check:

   request.method = HTTP method [OK]

Hint: Remember: method means GET, POST, PUT, DELETE [OK]

Common Mistakes:

• Confusing method with URL or path
• Thinking method is client IP
• Mixing method with response status

2. Which of the following is the correct way to access query parameters from a Flask request object?

easy

A. request.args.get('param')

B. request.form['param']

C. request.cookies['param']

D. request.headers['param']

Solution

1. Step 1: Identify how query parameters are accessed

   Query parameters are part of the URL after the question mark and are accessed via request.args.

2. Step 2: Use the correct method to get a parameter

   Using request.args.get('param') safely retrieves the value or returns None if missing.

3. Final Answer:

   request.args.get('param') -> Option A

4. Quick Check:

   Query params = request.args.get() [OK]

Hint: Query params use request.args.get('name') [OK]

Common Mistakes:

• Using request.form for query parameters
• Trying to get query params from cookies or headers
• Using request.args['param'] without .get() risking KeyError

3. Given this Flask route code snippet, what will be printed if a client sends a POST request with form data {'username': 'alice'}?

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

@app.route('/login', methods=['POST'])
def login():
    user = request.form.get('username')
    method = request.method
    return f"User: {user}, Method: {method}"

medium

A. User: alice, Method: POST

B. User: None, Method: GET

C. User: alice, Method: GET

D. User: None, Method: POST

Solution

1. Step 1: Understand the request method and form data

   The client sends a POST request with form data containing 'username' = 'alice'.

2. Step 2: Check how data is accessed in the code

   The code uses request.form.get('username') which retrieves 'alice', and request.method which is 'POST'.

3. Final Answer:

   User: alice, Method: POST -> Option A

4. Quick Check:

   Form data and method match output [OK]

Hint: Form data is in request.form; method is request.method [OK]

Common Mistakes:

• Assuming method is GET when POST was sent
• Using request.args instead of request.form for POST data
• Expecting None for existing form data

4. What is wrong with this Flask code snippet if it raises a KeyError when accessing request.form['email']?

@app.route('/submit', methods=['POST'])
def submit():
    email = request.form['email']
    return f"Email: {email}"

medium

A. Flask requires request.args for form data

B. The route should accept GET method instead of POST

C. The form data might not include 'email', causing KeyError

D. request.form cannot be accessed directly

Solution

1. Step 1: Understand why KeyError occurs

   Accessing request.form['email'] raises KeyError if 'email' is missing in the form data.

2. Step 2: Suggest safer access method

   Use request.form.get('email') to avoid KeyError and get None if missing.

3. Final Answer:

   The form data might not include 'email', causing KeyError -> Option C

4. Quick Check:

   Missing key in form causes KeyError [OK]

Hint: Use .get() to avoid KeyError on missing form keys [OK]

Common Mistakes:

• Assuming form always has the key
• Confusing form data with query parameters
• Thinking request.form is inaccessible

5. You want to check if a client sent a cookie named session_id in a Flask route. Which code snippet correctly checks for it and returns its value or 'No session' if missing? A)

sid = request.cookies['session_id']
return sid if sid else 'No session'

B)

sid = request.cookies.get('session_id')
return sid or 'No session'

C)

sid = request.form.get('session_id')
return sid or 'No session'

D)

sid = request.args.get('session_id')
return sid or 'No session'

hard

A. Access cookie directly with [] and check truthiness

B. Use .get() on cookies and return fallback if missing

C. Check form data for cookie value

D. Check query parameters for cookie value

Solution

1. Step 1: Identify how to safely access cookies

   Cookies are accessed via request.cookies. Using .get() avoids KeyError if cookie is missing.

2. Step 2: Return cookie value or fallback

   Using sid or 'No session' returns the cookie value if present, else the fallback string.

3. Final Answer:

   Use .get() on cookies and return fallback if missing -> Option B

4. Quick Check:

   Cookies use request.cookies.get() safely [OK]

Hint: Use request.cookies.get('name') to avoid errors [OK]

Common Mistakes:

• Accessing cookies with [] risking KeyError
• Looking for cookies in form or args
• Not providing fallback for missing cookie