Expiration-based caching in Rest API - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to set the cache expiration time to 60 seconds.

Rest API

cache.set('user_data', data, expire=[1])

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

A60

B600

C6

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using 0 which means no expiration.

Using 600 which is 10 minutes, not 1 minute.

The expiration time is set in seconds. 60 means the cache will expire after one minute.

2fill in blank

medium

Complete the code to check if the cached data has expired before returning it.

Rest API

if cache.get('user_data') is not [1]:
    return cache.get('user_data')

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

A0

BFalse

CTrue

DNone

Attempts:

3 left

💡 Hint

Common Mistakes

Checking for False instead of None.

Using 0 which is a valid value but not the absence of data.

When cache.get returns None, it means the data is not in cache or expired.

3fill in blank

hard

Fix the error in the code to correctly update the cache with new data and expiration.

Rest API

cache.[1]('user_data', new_data, expire=120)

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

Aset

Bupdate

Cput

Dadd

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'update' which may not exist.

Using 'add' which might only add if key doesn't exist.

The correct method to store data with expiration is 'set'.

4fill in blank

hard

Fill both blanks to create a cache dictionary comprehension that stores word lengths only for words longer than 3 characters.

Rest API

cache_data = {word: [1] for word in words if len(word) [2] 3}

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

Alen(word)

B>

C<=

Dword

Attempts:

3 left

💡 Hint

Common Mistakes

Using the word itself as value instead of its length.

Using '<=' instead of '>' causing wrong filtering.

We want the length of each word (len(word)) and only include words longer than 3 characters (len(word) > 3).

5fill in blank

hard

Fill all three blanks to create a cache dictionary comprehension that stores uppercase words as keys and their lengths as values, only if length is greater than 4.

Rest API

cache_data = { [1]: [2] for word in words if len(word) [3] 4 }

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

Aword.upper()

Blen(word)

C>

Dword.lower()

Attempts:

3 left

💡 Hint

Common Mistakes

Using word.lower() instead of word.upper() for keys.

Using '<' instead of '>' in the condition.

The keys are uppercase words (word.upper()), values are their lengths (len(word)), and we filter words longer than 4 characters (len(word) > 4).

Practice

1. What does the Cache-Control: max-age header do in expiration-based caching?

easy

A. It deletes the cache immediately after the response.

B. It disables caching for the resource.

C. It sets how long the cached data is considered fresh.

D. It forces the client to always fetch new data.

Solution

1. Step 1: Understand the role of Cache-Control header

   The Cache-Control header controls caching behavior for HTTP responses.

2. Step 2: Identify the meaning of max-age directive

   The max-age directive specifies the time in seconds that the response is considered fresh and can be served from cache.

3. Final Answer:

   It sets how long the cached data is considered fresh. -> Option C

4. Quick Check:

   max-age = cache freshness duration [OK]

Hint: Remember max-age sets cache freshness time in seconds [OK]

Common Mistakes:

• Confusing max-age with disabling cache
• Thinking max-age deletes cache immediately
• Assuming max-age forces fresh fetch every time

2. Which of the following is the correct syntax to set a cache expiration of 300 seconds in an HTTP response header?

easy

A. Cache-Control: maxage: 300

B. Cache-Control: max-age=300

C. Cache-Control: expire=300

D. Cache-Control: timeout=300

Solution

1. Step 1: Recall correct Cache-Control syntax

   The Cache-Control header uses directives separated by commas, with max-age specified as max-age=seconds.

2. Step 2: Compare options to correct syntax

   Only Cache-Control: max-age=300 uses the correct format: max-age=300.

3. Final Answer:

   Cache-Control: max-age=300 -> Option B

4. Quick Check:

   Correct header syntax = max-age=seconds [OK]

Hint: Use equal sign (=) with max-age, no spaces [OK]

Common Mistakes:

• Using colon instead of equal sign
• Using incorrect directive names like expire or timeout
• Adding spaces inside the directive

3. Given this HTTP response header:
Cache-Control: max-age=10
What will happen if a client requests the same resource 5 seconds later?

medium

A. The client will use the cached response without contacting the server.

B. The client will ignore the cache and fetch new data from the server.

C. The client will receive a 404 error.

D. The client will refresh the cache but still use old data.

Solution

1. Step 1: Understand max-age meaning

   max-age=10 means the cached data is fresh for 10 seconds after the first fetch.

2. Step 2: Check time elapsed since caching

   5 seconds is less than 10 seconds, so cache is still fresh and valid.

3. Final Answer:

   The client will use the cached response without contacting the server. -> Option A

4. Quick Check:

   Elapsed time < max-age = use cache [OK]

Hint: If request time < max-age, cache is used [OK]

Common Mistakes:

• Assuming cache expires immediately
• Thinking client always fetches new data
• Confusing max-age with cache invalidation

4. You set Cache-Control: max-age=60 but clients still fetch new data every time. What is the likely mistake?

medium

A. The client does not support caching headers.

B. The max-age value should be in milliseconds, not seconds.

C. The resource URL is missing a file extension.

D. The server is sending no-cache header overriding max-age.

Solution

1. Step 1: Check for conflicting headers

   If the server sends a no-cache directive, it forces clients to revalidate or fetch fresh data despite max-age.

2. Step 2: Understand max-age units and client support

   max-age is in seconds, and most clients support caching headers, so these are unlikely causes.

3. Final Answer:

   The server is sending no-cache header overriding max-age. -> Option D

4. Quick Check:

   no-cache overrides max-age [OK]

Hint: Check for no-cache header overriding max-age [OK]

Common Mistakes:

• Confusing seconds with milliseconds for max-age
• Blaming client support without checking headers
• Assuming URL format affects caching

5. You want to cache API responses for 5 minutes but ensure clients always get fresh data after expiration. Which header setup is best?

hard

A. Cache-Control: max-age=300, must-revalidate

B. Cache-Control: max-age=300, no-store

C. Cache-Control: no-cache, max-age=300

D. Cache-Control: max-age=0, public

Solution

1. Step 1: Understand caching for 5 minutes

   max-age=300 sets cache freshness for 300 seconds (5 minutes).

2. Step 2: Ensure fresh data after expiration

   must-revalidate forces clients to check with server after max-age expires before using cached data.

3. Step 3: Evaluate other options

   no-store disables caching, no-cache forces revalidation every time, max-age=0 means no caching.

4. Final Answer:

   Cache-Control: max-age=300, must-revalidate -> Option A

5. Quick Check:

   max-age + must-revalidate = cache then fresh after expiry [OK]

Hint: Use must-revalidate with max-age for fresh data after expiry [OK]

Common Mistakes:

• Using no-store disables caching completely
• Using no-cache forces revalidation every request
• Setting max-age=0 disables caching