Caching strategies in FastAPI - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the FastAPI cache dependency.

FastAPI

from fastapi import FastAPI
from fastapi_cache import [1]

app = FastAPI()

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

ACacheManager

BCacheControl

CCache

DFastAPICache

Attempts:

3 left

💡 Hint

Common Mistakes

Using a wrong class name like Cache or CacheControl.

Trying to import from fastapi instead of fastapi_cache.

The correct import for FastAPI caching is FastAPICache from fastapi_cache.

2fill in blank

medium

Complete the code to set up an in-memory cache backend.

FastAPI

from fastapi_cache.backends.inmemory import [1]

cache_backend = [1]()

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

AInMemoryBackend

BMemoryCache

CInMemoryCache

DMemoryBackend

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'MemoryCache' or 'InMemoryCache' which do not exist.

Confusing backend with cache class names.

The in-memory backend class is called InMemoryBackend.

3fill in blank

hard

Fix the error in the cache decorator to set expiration time to 60 seconds.

FastAPI

@app.get('/items')
@cache(expire=[1])
async def get_items():
    return ['apple', 'banana']

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

A'60'

B6000

C60

D'sixty'

Attempts:

3 left

💡 Hint

Common Mistakes

Passing the number as a string like '60'.

Using a wrong number like 6000 or a word.

The expire parameter expects an integer number of seconds, so 60 without quotes is correct.

4fill in blank

hard

Fill both blanks to initialize the cache with the backend and FastAPI app.

FastAPI

from fastapi_cache import FastAPICache

FastAPICache.[1](cache_backend, prefix=[2])

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

Ainit

Bstart

C"fastapi-cache"

D"cache"

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'start' instead of 'init'.

Using a prefix with quotes missing or wrong string.

Use init to initialize the cache and set a prefix string like "cache".

5fill in blank

hard

Fill all three blanks to create a cached endpoint with a 120-second expiration.

FastAPI

@app.get('/data')
@FastAPICache.[1](expire=[2])
async def get_data():
    return [3]

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

Acache

B120

C['data1', 'data2']

Dcached

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong decorator name like 'cached'.

Passing expiration as string instead of number.

Returning a wrong data type.

The decorator is cache, expiration is 120 seconds, and the function returns a list of data.

Practice

1. What is the main purpose of using caching in a FastAPI application?

easy

A. To increase the size of the application code

B. To remove all data from the server

C. To make the app slower for testing

D. To save repeated work and speed up response times

Solution

1. Step 1: Understand caching concept

   Caching stores results of expensive operations to reuse later.

2. Step 2: Identify caching benefit in FastAPI

   This reuse saves repeated work and speeds up response times.

3. Final Answer:

   To save repeated work and speed up response times -> Option D

4. Quick Check:

   Caching purpose = speed up responses [OK]

Hint: Caching means saving work to respond faster [OK]

Common Mistakes:

• Thinking caching increases code size
• Believing caching slows down the app
• Confusing caching with deleting data

2. Which of the following is the correct way to apply caching with expiration in FastAPI using the decorator?

easy

A. @cache(expire=60)

B. @cache_time(60)

C. @cache(expiration=60)

D. @cache(60_seconds)

Solution

1. Step 1: Recall FastAPI cache decorator syntax

   The correct decorator is @cache(expire=seconds) to set expiration time.

2. Step 2: Match options with correct syntax

   Only @cache(expire=60) matches the correct pattern.

3. Final Answer:

   @cache(expire=60) -> Option A

4. Quick Check:

   Decorator with expire=60 is correct [OK]

Hint: Use @cache with expire=seconds for expiration [OK]

Common Mistakes:

• Using wrong decorator names like @cache_time
• Using incorrect parameter names like expiration
• Passing expiration time without parameter name

3. Given this FastAPI code snippet, what will be the output on the second call to /data within 10 seconds?

from fastapi import FastAPI
from fastapi_cache.decorator import cache

app = FastAPI()

@cache(expire=10)
async def get_data():
    print('Fetching data')
    return {'value': 42}

@app.get('/data')
async def data():
    return await get_data()

medium

A. {'value': 42} and prints 'Fetching data' once only

B. {'value': 42} and prints 'Fetching data' every call

C. Error because cache decorator is missing setup

D. Empty response because cache expired immediately

Solution

1. Step 1: Check for cache initialization

   The code uses @cache but lacks FastAPICache.init with a backend on startup.

2. Step 2: Analyze execution

   Without init, FastAPICache.get raises AttributeError on first call, before executing get_data or printing.

3. Final Answer:

   Error because cache decorator is missing setup -> Option C

4. Quick Check:

   Missing FastAPICache.init causes runtime error [OK]

Hint: Cache decorator requires FastAPICache.init on startup [OK]

Common Mistakes:

• Assuming caching works without FastAPICache.init, print once only
• Thinking no caching, print every call
• Believing cache expires immediately

4. Identify the error in this FastAPI caching setup:

from fastapi import FastAPI
from fastapi_cache import FastAPICache
from fastapi_cache.backends.inmemory import InMemoryBackend

app = FastAPI()

@app.on_event('startup')
async def startup():
    FastAPICache.init(InMemoryBackend())

@cache(expire=30)
async def get_info():
    return {'info': 'cached data'}

medium

A. InMemoryBackend requires a Redis URL parameter

B. Cache decorator is used without importing it

C. Missing await keyword when calling FastAPICache.init

D. Startup event should be named 'start' instead of 'startup'

Solution

1. Step 1: Check imports for cache decorator

   The code uses @cache but does not import it from fastapi_cache.decorator.

2. Step 2: Verify other parts for correctness

   FastAPICache.init is correctly called; InMemoryBackend needs no parameters; event name 'startup' is correct.

3. Final Answer:

   Cache decorator is used without importing it -> Option B

4. Quick Check:

   Missing import of cache decorator causes error [OK]

Hint: Always import @cache decorator before using it [OK]

Common Mistakes:

• Forgetting to import cache decorator
• Passing Redis URL to InMemoryBackend
• Renaming startup event incorrectly

5. You want to cache user profile data in FastAPI using Redis backend with a 5-minute expiration. Which setup correctly initializes caching and applies it to the get_user_profile function?

from fastapi import FastAPI
from fastapi_cache import FastAPICache
from fastapi_cache.backends.redis import RedisBackend
from fastapi_cache.decorator import cache
import aioredis

app = FastAPI()

@app.on_event('startup')
async def startup():
    redis = aioredis.from_url('redis://localhost')
    FastAPICache.init(RedisBackend(redis), prefix='fastapi-cache')

@cache(expire=300)
async def get_user_profile(user_id: int):
    # Simulate fetching user profile
    return {'user_id': user_id, 'name': 'Alice'}

hard

A. Correct setup: Redis backend initialized with aioredis, cache decorator with expire=300

B. Incorrect: RedisBackend needs a string URL, not aioredis instance

C. Incorrect: Cache decorator expire should be in milliseconds, not seconds

D. Incorrect: FastAPICache.init must be called inside the cached function

Solution

1. Step 1: Verify Redis backend initialization

   Using aioredis.from_url and passing RedisBackend(redis) is correct for Redis caching.

2. Step 2: Check cache decorator usage

   @cache(expire=300) sets 5 minutes expiration correctly in seconds.

3. Final Answer:

   Correct setup: Redis backend initialized with aioredis, cache decorator with expire=300 -> Option A

4. Quick Check:

   Redis backend + expire=300 seconds = correct caching [OK]

Hint: Use aioredis instance with RedisBackend and expire in seconds [OK]

Common Mistakes:

• Passing Redis URL string directly instead of aioredis instance
• Using expire in milliseconds instead of seconds
• Calling FastAPICache.init inside cached function