Cache framework configuration in Django - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What is the output of this Django cache configuration?

Given the following Django cache settings, what will be the cache timeout for the default cache?

Django

CACHES = {
    'default': {
        'BACKEND': 'django.core.cache.backends.locmem.LocMemCache',
        'LOCATION': 'unique-snowflake',
        'TIMEOUT': 300,
    }
}

cache_timeout = CACHES['default']['TIMEOUT']

A 300

B None

C 0

D 60

💡 Hint

Look at the TIMEOUT value set in the default cache dictionary.

The TIMEOUT key in the cache configuration sets the cache expiration time in seconds. Here it is set to 300 seconds.

📝 Syntax

intermediate

Which cache backend setting is syntactically correct?

Identify the correct Django cache backend setting syntax.

A 'BACKEND': 'django.core.cache.backends.memcached.MemcacheCache'

B 'BACKEND': 'django.core.cache.backends.memcached.Memcached'

C 'BACKEND': 'django.core.cache.backends.memcached.MemcachedCache'

D 'BACKEND': 'django.core.cache.backends.memcached.CacheMemcached'

💡 Hint

Check the official Django cache backend class names.

The correct backend class for Memcached in Django is 'MemcachedCache'. Other options are invalid class names.

🔧 Debug

advanced

Why does this cache configuration raise an error?

Examine the following cache configuration and identify the cause of the error.

Django

CACHES = {
    'default': {
        'BACKEND': 'django.core.cache.backends.locmem.LocMemCache',
        'LOCATION': 'unique-snowflake',
        'TIMEOUT': 300,
    }
}

A TIMEOUT cannot be set in cache configuration

B Invalid backend name causes ImportError

C LOCATION value must be an integer, not string

D Missing comma after 'LocMemCache' string causes SyntaxError

💡 Hint

Look carefully at the dictionary syntax between keys.

The missing comma after the 'BACKEND' value causes a syntax error in the dictionary definition.

❓ state_output

advanced

What is the value of cache key after this code runs?

Given this Django cache usage code, what will be the value of 'my_key' in the cache after execution?

Django

from django.core.cache import cache

cache.set('my_key', 'hello', timeout=10)
cache.set('my_key', 'world', timeout=None)
value = cache.get('my_key')

A 'world'

B 'hello'

C None

D Raises KeyError

💡 Hint

The second set call overwrites the first with no timeout.

The second cache.set call replaces the value with 'world' and sets timeout to None, meaning it never expires.

🧠 Conceptual

expert

Which cache configuration ensures thread-safe in-memory caching in Django?

Select the cache backend configuration that provides thread-safe in-memory caching suitable for development.

A {'BACKEND': 'django.core.cache.backends.memcached.PyMemcacheCache', 'LOCATION': '127.0.0.1:11211'}

B {'BACKEND': 'django.core.cache.backends.locmem.LocMemCache', 'LOCATION': 'unique-snowflake'}

C {'BACKEND': 'django.core.cache.backends.filebased.FileBasedCache', 'LOCATION': '/var/tmp/django_cache'}

D {'BACKEND': 'django.core.cache.backends.dummy.DummyCache'}

💡 Hint

Consider which backend is designed for thread-safe local memory caching.

LocMemCache is thread-safe and stores cache in local memory, ideal for development and testing.

Practice

1. What is the main purpose of configuring the CACHES setting in Django?

easy

A. To define the database connection details

B. To tell Django where and how to store temporary data for faster access

C. To set the URL routing rules

D. To configure user authentication methods

Solution

1. Step 1: Understand the role of caching

   Caching stores temporary data to speed up repeated requests by avoiding repeated work.

2. Step 2: Identify what CACHES configures

   The CACHES setting tells Django which backend to use and where to store cached data.

3. Final Answer:

   To tell Django where and how to store temporary data for faster access -> Option B

4. Quick Check:

   Cache config = store temp data [OK]

Hint: Cache config sets storage for temporary data [OK]

Common Mistakes:

• Confusing cache with database settings
• Thinking cache controls URL routing
• Mixing cache with authentication settings

2. Which of the following is the correct way to define a simple in-memory cache backend in Django's CACHES setting?

easy

A. 'default': {'BACKEND': 'django.core.cache.backends.locmem.LocMemCache'}

B. 'default': {'BACKEND': 'django.core.cache.backends.filebased.FileBasedCache', 'LOCATION': '/var/tmp/django_cache'}

C. 'default': {'BACKEND': 'django.core.cache.backends.memcached.MemcachedCache', 'LOCATION': '127.0.0.1:11211'}

D. 'default': {'BACKEND': 'django.core.cache.backends.db.DatabaseCache', 'LOCATION': 'my_cache_table'}

Solution

1. Step 1: Identify the in-memory cache backend

   The in-memory cache backend in Django is LocMemCache, which stores cache in local memory.

2. Step 2: Match the correct syntax

   'default': {'BACKEND': 'django.core.cache.backends.locmem.LocMemCache'} correctly sets BACKEND to django.core.cache.backends.locmem.LocMemCache without needing a LOCATION.

3. Final Answer:

   'default': {'BACKEND': 'django.core.cache.backends.locmem.LocMemCache'} -> Option A

4. Quick Check:

   In-memory cache = LocMemCache [OK]

Hint: LocMemCache is in-memory, no location needed [OK]

Common Mistakes:

• Adding LOCATION for LocMemCache unnecessarily
• Confusing file-based or DB cache for in-memory
• Using wrong backend string casing

3. Given this Django cache configuration snippet, what will be the cache backend used?

 CACHES = {
    'default': {
        'BACKEND': 'django.core.cache.backends.memcached.PyMemcacheCache',
        'LOCATION': '127.0.0.1:11211',
    }
}

medium

A. File-based cache storing data in /var/tmp

B. Local memory cache inside the Django process

C. Database cache storing data in a DB table

D. Memcached cache using PyMemcache client on localhost

Solution

1. Step 1: Read the BACKEND value

   The backend is set to django.core.cache.backends.memcached.PyMemcacheCache, which uses Memcached with the PyMemcache client.

2. Step 2: Check the LOCATION

   The location is 127.0.0.1:11211, the default Memcached server address on localhost.

3. Final Answer:

   Memcached cache using PyMemcache client on localhost -> Option D

4. Quick Check:

   Memcached backend = PyMemcache + localhost [OK]

Hint: Memcached backend with PyMemcache uses localhost:11211 [OK]

Common Mistakes:

• Confusing Memcached with file or DB cache
• Ignoring the LOCATION setting
• Assuming local memory cache instead

4. Identify the error in this Django cache configuration snippet:

 CACHES = {
    'default': {
        'BACKEND': 'django.core.cache.backends.locmem.LocMemCache',
        'LOCATION': '/tmp/django_cache'
    }
}

medium

A. LocMemCache backend should not have a LOCATION setting

B. The BACKEND string is misspelled

C. LOCATION path must be a database table name

D. The CACHES dictionary must be a list instead

Solution

1. Step 1: Understand LocMemCache usage

   LocMemCache stores cache in local memory and does not use a file path or location setting.

2. Step 2: Identify the incorrect LOCATION key

   Providing a LOCATION with a file path is invalid for LocMemCache and will cause an error.

3. Final Answer:

   LocMemCache backend should not have a LOCATION setting -> Option A

4. Quick Check:

   LocMemCache no LOCATION needed [OK]

Hint: LocMemCache ignores LOCATION, so don't set it [OK]

Common Mistakes:

• Adding LOCATION to LocMemCache
• Confusing file cache with memory cache
• Misunderstanding backend string format

5. You want to configure Django to use a database table named my_cache_table for caching. Which is the correct CACHES setting to achieve this?

hard

A. 'default': {'BACKEND': 'django.core.cache.backends.memcached.MemcachedCache', 'LOCATION': 'my_cache_table'}

B. 'default': {'BACKEND': 'django.core.cache.backends.filebased.FileBasedCache', 'LOCATION': 'my_cache_table'}

C. 'default': {'BACKEND': 'django.core.cache.backends.db.DatabaseCache', 'LOCATION': 'my_cache_table'}

D. 'default': {'BACKEND': 'django.core.cache.backends.locmem.LocMemCache', 'LOCATION': 'my_cache_table'}

Solution

1. Step 1: Identify the backend for database caching

   The backend for caching in a database table is DatabaseCache.

2. Step 2: Set the LOCATION to the table name

   The LOCATION must be the name of the database table, here my_cache_table.

3. Final Answer:

   'default': {'BACKEND': 'django.core.cache.backends.db.DatabaseCache', 'LOCATION': 'my_cache_table'} -> Option C

4. Quick Check:

   DB cache backend + table name = correct config [OK]

Hint: DatabaseCache backend uses table name as LOCATION [OK]

Common Mistakes:

• Using file or memory cache backend for DB caching
• Setting LOCATION to a file path instead of table name
• Confusing Memcached with DB cache