Low-level cache API in Django - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the cache object from Django's cache framework.

Django

from django.core.cache import [1]

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

ACacheHandler

Bcaches

Ccache_control

Dcache

Attempts:

3 left

💡 Hint

Common Mistakes

Importing caches instead of cache when only one cache is used.

Trying to import cache_control which is unrelated.

The cache object is imported from django.core.cache to use the low-level cache API.

2fill in blank

medium

Complete the code to set a cache key 'greeting' with value 'hello' that expires in 30 seconds.

Django

cache.[1]('greeting', 'hello', timeout=30)

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

Aget

Bset

Cdelete

Dclear

Attempts:

3 left

💡 Hint

Common Mistakes

Using get which only retrieves data.

Using delete which removes data.

The set method stores a value in the cache with an optional timeout.

3fill in blank

hard

Fix the error in the code to retrieve the value of cache key 'greeting'.

Django

value = cache.[1]('greeting')

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

Aadd

Bset

Cget

Dfetch

Attempts:

3 left

💡 Hint

Common Mistakes

Using set which stores data instead of retrieving.

Using fetch which is not a valid cache method.

The get method retrieves the value stored under a cache key.

4fill in blank

hard

Fill both blanks to delete a cache key 'greeting' and then clear all cache keys.

Django

cache.[1]('greeting')
cache.[2]()

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

Adelete

Bclear

Cset

Dget

Attempts:

3 left

💡 Hint

Common Mistakes

Using set or get instead of delete or clear.

Mixing up the order of methods.

The delete method removes a specific cache key, and clear removes all keys.

5fill in blank

hard

Fill all three blanks to add a cache key 'counter' with value 1 only if it does not exist, then increment it by 1.

Django

cache.[1]('counter', 1)
counter = cache.[2]('counter')
counter = counter [3] 1

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

Aadd

Bget

C+

Dset

Attempts:

3 left

💡 Hint

Common Mistakes

Using set instead of add which overwrites existing keys.

Trying to increment the key directly without retrieving.

The add method sets a key only if it does not exist. Then get retrieves it, and + increments the value.

Practice

1. What is the main purpose of Django's low-level cache API?

easy

A. To store and retrieve data quickly to improve app speed

B. To manage database migrations automatically

C. To handle user authentication and permissions

D. To create HTML templates for web pages

Solution

1. Step 1: Understand the cache API role

   The low-level cache API is designed to store data temporarily for fast access.

2. Step 2: Compare with other options

   Other options relate to different Django features like migrations, auth, or templates, not caching.

3. Final Answer:

   To store and retrieve data quickly to improve app speed -> Option A

4. Quick Check:

   Cache API purpose = speed up data access [OK]

Hint: Cache API is for fast data storage and retrieval [OK]

Common Mistakes:

• Confusing cache with database migrations
• Mixing cache with authentication features
• Thinking cache creates HTML templates

2. Which of the following is the correct way to save a value in Django's low-level cache?

easy

A. cache.set('key', 'value')

B. cache.save('key', 'value')

C. cache.put('key', 'value')

D. cache.store('key', 'value')

Solution

1. Step 1: Recall the cache API method for saving

   The correct method to save data in Django cache is cache.set.

2. Step 2: Verify other options

   Methods like save, put, and store do not exist in Django's cache API.

3. Final Answer:

   cache.set('key', 'value') -> Option A

4. Quick Check:

   Use cache.set to save data [OK]

Hint: Use cache.set to save data in cache [OK]

Common Mistakes:

• Using cache.save instead of cache.set
• Confusing cache methods with other APIs
• Assuming put or store exist in cache API

3. What will be the output of this code snippet?

from django.core.cache import cache
cache.set('count', 5)
value = cache.get('count')
print(value)

medium

A. 0

B. None

C. KeyError

D. 5

Solution

1. Step 1: Analyze cache.set usage

   The code sets the key 'count' with value 5 in the cache.

2. Step 2: Analyze cache.get usage

   Retrieving 'count' returns the stored value 5, so print outputs 5.

3. Final Answer:

   5 -> Option D

4. Quick Check:

   cache.get returns stored value 5 [OK]

Hint: cache.get returns stored value or None if missing [OK]

Common Mistakes:

• Expecting None if key was just set
• Thinking cache.get raises KeyError
• Confusing default return values

4. Identify the error in this code snippet using Django's low-level cache API:

from django.core.cache import cache
cache.set('user', 'Alice')
value = cache.get('user', 'Bob')
print(value)

medium

A. cache.get does not accept a default value

B. cache.set requires a timeout argument

C. No error; output will be 'Alice'

D. cache.get will raise an exception if key exists

Solution

1. Step 1: Check cache.set usage

   cache.set with key and value is valid; timeout is optional.

2. Step 2: Check cache.get with default

   cache.get accepts a default value returned if key is missing; here key exists, so returns 'Alice'.

3. Final Answer:

   No error; output will be 'Alice' -> Option C

4. Quick Check:

   cache.get returns stored value if key exists [OK]

Hint: cache.get default used only if key missing [OK]

Common Mistakes:

• Thinking cache.get can't take default
• Believing timeout is mandatory for cache.set
• Assuming cache.get raises error if key exists

5. You want to cache a user's profile data for 10 minutes using Django's low-level cache API. Which code snippet correctly does this?

hard

A. cache.set('profile_1', user_profile, expire=600)

B. cache.set('profile_1', user_profile, timeout=600)

C. cache.save('profile_1', user_profile, timeout=600)

D. cache.set('profile_1', user_profile, time=600)

Solution

1. Step 1: Identify correct timeout argument

   The cache.set method uses the argument timeout to specify cache duration in seconds.

2. Step 2: Check method and argument names

   Only cache.set('profile_1', user_profile, timeout=600) uses cache.set with timeout=600. Others use wrong method or argument names.

3. Final Answer:

   cache.set('profile_1', user_profile, timeout=600) -> Option B

4. Quick Check:

   Use cache.set with timeout for timed caching [OK]

Hint: Use timeout parameter in cache.set for expiry [OK]

Common Mistakes:

• Using expire or time instead of timeout
• Using cache.save which doesn't exist
• Omitting timeout for temporary cache