Low-level cache API in Django - Step-by-Step Execution

Concept Flow - Low-level cache API

Start

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Call cache.set(key, value, timeout)

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Store value in cache with key

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Call cache.get(key)

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Retrieve value if exists and not expired

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Return value or None

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Call cache.delete(key)

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Remove key from cache

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End

This flow shows how Django's low-level cache API stores, retrieves, and deletes cached data using keys.

Execution Sample

Django

from django.core.cache import cache
cache.set('greet', 'Hello', 10)
value = cache.get('greet')
cache.delete('greet')
value_after_delete = cache.get('greet')

This code sets a cache key 'greet' with value 'Hello' for 10 seconds, retrieves it, deletes it, then tries to retrieve again.

Execution Table

Step	Action	Key	Value Stored/Retrieved	Cache State	Output
1	cache.set	greet	'Hello'	{'greet': 'Hello'}	True
2	cache.get	greet	N/A	{'greet': 'Hello'}	'Hello'
3	cache.delete	greet	N/A	{}	True
4	cache.get	greet	N/A	{}	None

💡 Cache is empty after deletion; get returns None.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4
cache contents	{}	{'greet': 'Hello'}	{'greet': 'Hello'}	{}	{}
value	N/A	N/A	'Hello'	'Hello'	None
value_after_delete	N/A	N/A	N/A	N/A	None

Key Moments - 2 Insights

Why does cache.get return None after cache.delete even though the key existed before?

Because cache.delete removes the key from the cache, so subsequent cache.get calls find no value (see step 3 and 4 in execution_table).

What happens if you call cache.get with a key that was never set?

cache.get returns None because the key does not exist in the cache (similar to step 4 in execution_table).

Visual Quiz - 3 Questions

Look at the execution table, what is the output of cache.get('greet') at step 2?

A Error

B None

C 'Hello'

D '' (empty string)

💡 Hint

Check the Output column at step 2 in the execution_table.

At which step does the cache become empty?

A Step 1

B Step 3

C Step 2

D Step 4

💡 Hint

Look at the Cache State column in execution_table to see when '{}' appears.

If cache.set('greet', 'Hi', 5) is called instead of step 1, what changes in the execution_table?

A Value stored changes to 'Hi' at step 1

B Cache state becomes empty at step 1

C Output at step 2 becomes None

D No change at all

💡 Hint

Focus on the Value Stored/Retrieved column at step 1.

Concept Snapshot

Django Low-level Cache API:
- Use cache.set(key, value, timeout) to store data.
- Use cache.get(key) to retrieve data or None if missing.
- Use cache.delete(key) to remove data.
- Cache stores key-value pairs temporarily.
- Useful for speeding up repeated data access.

Full Transcript

This visual trace shows how Django's low-level cache API works step-by-step. First, cache.set stores a value with a key and timeout. Then cache.get retrieves the value if it exists. cache.delete removes the key and its value. After deletion, cache.get returns None because the key no longer exists. Variables like cache contents and retrieved values change accordingly. This helps beginners see how caching stores and removes data in Django.