Accessing query parameters in Flask - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output when accessing a query parameter in Flask?

Consider this Flask route that reads a query parameter named name. What will be the output if the URL is /greet?name=Alice?

Flask

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

@app.route('/greet')
def greet():
    user = request.args.get('name', 'Guest')
    return f'Hello, {user}!'

# Assume the server is running and the URL accessed is /greet?name=Alice

A Hello, None!

B Hello, Alice!

C Error: 'name' parameter missing

D Hello, Guest!

💡 Hint

Check how request.args.get works with default values.

The request.args.get('name', 'Guest') fetches the query parameter name. If it exists, it returns its value; otherwise, it returns the default 'Guest'. Since the URL has name=Alice, it returns 'Alice'.

📝 Syntax

intermediate

Which option correctly accesses multiple query parameters in Flask?

You want to access two query parameters, user and age, from the URL /info?user=Bob&age=30. Which code snippet correctly retrieves both parameters?

Flask

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

@app.route('/info')
def info():
    # Fill in the blanks
    user = ???
    age = ???
    return f'User: {user}, Age: {age}'

A

user = request.args.get('user')
age = request.args.get('age')

B

user = request.form.get('user')
age = request.form.get('age')

C

user = request.args['user']
age = request.args['age']

D

user = request.values.get('user')
age = request.values.get('age')

💡 Hint

Remember that query parameters are part of the URL, not form data.

request.args.get() safely retrieves query parameters with optional default values. Using request.form is for POST form data, so it won't work here. request.values combines args and form but is less explicit.

🔧 Debug

advanced

Why does this Flask code fail to get the query parameter?

This Flask route is supposed to greet a user by name from the query parameter, but it always returns 'Hello, Guest!'. What is the cause?

Flask

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

@app.route('/hello')
def hello():
    name = request.form.get('name', 'Guest')
    return f'Hello, {name}!'

# URL accessed: /hello?name=Eve

A Using request.form.get instead of request.args.get for query parameters

B The route decorator is missing methods=['GET']

C The default value 'Guest' is overriding the parameter

D The URL should use POST method to send parameters

💡 Hint

Check where query parameters are stored in Flask's request object.

Query parameters are accessed via request.args. request.form is for POST form data. Since the URL uses GET with query parameters, request.form.get('name') returns None, so default 'Guest' is used.

❓ state_output

advanced

What is the value of page after this Flask route runs?

Given this Flask route, what will be the value of page if the URL is /search (no query parameters)?

Flask

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

@app.route('/search')
def search():
    page = request.args.get('page', 1, type=int)
    return f'Page number: {page}'

A None

B '1'

C 1

D 0

💡 Hint

Look at the default value and the type conversion.

The request.args.get method returns the default value 1 as an integer because of type=int. Since no page parameter is in the URL, it uses the default integer 1.

🧠 Conceptual

expert

Which statement about accessing query parameters in Flask is TRUE?

Select the correct statement about how Flask handles query parameters in request.args:

A <code>request.args</code> can be modified to add new query parameters during request handling

B <code>request.args</code> is a dictionary that returns a list of values for each key by default

C <code>request.args.get('key')</code> raises a KeyError if the key is missing

D <code>request.args.getlist('key')</code> returns all values for a query parameter that appears multiple times

💡 Hint

Think about how Flask handles multiple values for the same query parameter.

request.args is an ImmutableMultiDict. It returns the first value for a key by default. To get all values for a repeated key, use getlist(). It does not raise KeyError on missing keys but returns None or default. It is immutable, so you cannot modify it.

Practice

1. In Flask, which method is used to safely access a query parameter named user from the URL?

easy

A. request.form['user']

B. request.args.get('user')

C. request.query['user']

D. request.params.get('user')

Solution

1. Step 1: Understand Flask request object

   Flask's request object holds incoming request data, including query parameters in args.

2. Step 2: Use the correct method to access query parameters

   request.args.get('user') safely retrieves the value of the user parameter or returns None if missing.

3. Final Answer:

   request.args.get('user') -> Option B

4. Quick Check:

   Use args.get() for query parameters [OK]

Hint: Use request.args.get('param') to read query parameters [OK]

Common Mistakes:

• Using request.form for query parameters
• Trying to access request.query which doesn't exist
• Using request.params instead of request.args

2. Which of the following is the correct syntax to get a query parameter page with a default value of 1 in Flask?

easy

A. request.args.get('page', default=1)

B. request.args.get('page', 1)

C. request.args['page'] or 1

D. request.args.get('page', fallback=1)

Solution

1. Step 1: Check the get() method parameters

   The get() method accepts a default keyword argument to provide a fallback value if the parameter is missing.

2. Step 2: Identify correct syntax for default

   Using request.args.get('page', default=1) correctly sets 1 as default. Passing 1 as second positional argument is invalid.

3. Final Answer:

   request.args.get('page', default=1) -> Option A

4. Quick Check:

   Use default= for fallback in get() [OK]

Hint: Use default= in get() to set fallback value [OK]

Common Mistakes:

• Passing default value as second positional argument
• Using fallback= which is not valid in Flask
• Accessing with [] which raises error if missing

3. What will be the output of this Flask route when accessed with URL /search?term=flask?

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

@app.route('/search')
def search():
    term = request.args.get('term', 'none')
    return f"Search term: {term}"

medium

A. Error: term parameter missing

B. Search term: none

C. Search term:

D. Search term: flask

Solution

1. Step 1: Understand the URL query parameter

   The URL contains ?term=flask, so the query parameter term has value 'flask'.

2. Step 2: Check how term is retrieved in code

   request.args.get('term', 'none') returns 'flask' because the parameter exists.

3. Final Answer:

   Search term: flask -> Option D

4. Quick Check:

   Parameter present returns its value, not default [OK]

Hint: If parameter exists, get() returns its value, else default [OK]

Common Mistakes:

• Assuming default is returned even if parameter exists
• Confusing query parameters with form data
• Expecting empty string instead of actual value

4. Identify the error in this Flask code snippet that tries to get a query parameter id:

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

@app.route('/item')
def item():
    id = request.args['id']
    return f"Item ID: {id}"

medium

A. Using request.args['id'] raises KeyError if 'id' missing

B. Missing import of request module

C. Route decorator syntax is incorrect

D. Using f-string inside return is invalid

Solution

1. Step 1: Analyze how query parameter is accessed

   Using request.args['id'] accesses the parameter directly and raises KeyError if missing.

2. Step 2: Identify safer alternative

   Using request.args.get('id') avoids error by returning None if missing.

3. Final Answer:

   Using request.args['id'] raises KeyError if 'id' missing -> Option A

4. Quick Check:

   Direct dict access can cause KeyError [OK]

Hint: Use get() to avoid KeyError when parameter might be missing [OK]

Common Mistakes:

• Assuming request.args['id'] never fails
• Ignoring possibility of missing parameters
• Confusing import errors with runtime errors

5. You want to create a Flask route /filter that reads two optional query parameters: category (default 'all') and limit (default 10, integer). Which code correctly handles both parameters safely?

hard

A. category = request.args.get('category') or 'all'
limit = int(request.args.get('limit', 10))

B. category = request.args['category'] or 'all'
limit = int(request.args['limit'] or 10)

C. category = request.args.get('category', default='all')
limit = int(request.args.get('limit', default=10))

D. category = request.args.get('category', 'all')
limit = int(request.args.get('limit', '10'))

Solution

1. Step 1: Handle category parameter with default

   Using request.args.get('category', default='all') safely returns 'all' if missing.

2. Step 2: Handle limit parameter with default and convert to int

   request.args.get('limit', default=10) returns string or int 10; wrapping with int() converts string to integer safely.

3. Step 3: Check other options for errors

   category = request.args['category'] or 'all' limit = int(request.args['limit'] or 10) risks KeyError; category = request.args.get('category') or 'all' limit = int(request.args.get('limit', 10)) uses positional default incorrectly; category = request.args.get('category', 'all') limit = int(request.args.get('limit', '10')) converts default string '10' which works but less clear than int 10.

4. Final Answer:

   category = request.args.get('category', default='all')\nlimit = int(request.args.get('limit', default=10)) -> Option C

5. Quick Check:

   Use get() with default and convert types explicitly [OK]

Hint: Use get() with default and convert types explicitly [OK]

Common Mistakes:

• Using [] which raises error if missing
• Passing default as positional argument incorrectly
• Not converting string query param to int