Redis with Python (redis-py) - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the output of this Redis-py command?

Given a Redis instance with a key 'counter' set to '10', what will be the output of the following Python code?

import redis
r = redis.Redis()
result = r.incr('counter')
print(result)

Redis

import redis
r = redis.Redis()
result = r.incr('counter')
print(result)

A 11

B 10

C TypeError

D None

💡 Hint

The INCR command increases the integer value stored at key by one and returns the new value.

The INCR command increments the value stored at 'counter' by 1. Since it was 10, the new value is 11, which is returned and printed.

📝 Syntax

intermediate

Which option correctly sets a key with expiration using redis-py?

You want to set a key 'session' with value 'abc123' that expires after 60 seconds. Which code snippet is correct?

A r.set('session', 'abc123', ex=60)

B r.set('session', 'abc123', expire=60)

C r.set('session', 'abc123', timeout=60)

D r.set('session', 'abc123', ttl=60)

💡 Hint

Check the redis-py documentation for the parameter name to set expiration in seconds.

The correct parameter to set expiration time in seconds in redis-py set() method is 'ex'. Other options are invalid and cause errors.

❓ optimization

advanced

How to efficiently retrieve multiple keys in redis-py?

You need to get the values of keys 'key1', 'key2', and 'key3' from Redis. Which approach is the most efficient?

A for k in ['key1', 'key2', 'key3']: r.get(k)

B r.get('key1'), r.get('key2'), r.get('key3')

C r.mget(['key1', 'key2', 'key3'])

D r.pipeline().get('key1').get('key2').get('key3').execute()

💡 Hint

Look for a redis-py command that fetches multiple keys in one call.

The mget() method fetches multiple keys in a single call, reducing network overhead. Option C uses pipeline but is more complex and less direct.

🔧 Debug

advanced

Why does this redis-py code raise a TypeError?

Consider this code snippet:

r.set('count', 5)
value = r.incr('count')
print(value)

Why does it raise a TypeError?

Redis

r.set('count', 5)
value = r.incr('count')
print(value)

A Because r.incr only works on keys that do not exist

B Because r.incr cannot increment a key set with a string

C Because r.set stores the integer as bytes, causing incr to fail

D Because r.set expects a string value, not an integer

💡 Hint

Check the data type of the value passed to r.set and what redis-py expects.

r.set expects the value to be bytes or string. Passing an integer directly causes a TypeError. You should convert the integer to string or bytes.

🧠 Conceptual

expert

What happens if you call r.get() on a non-existent key in redis-py?

If you run r.get('missing_key') on a Redis instance where 'missing_key' does not exist, what is the result?

Redis

r.get('missing_key')

A Raises a KeyError

B Returns None

C Returns an empty string ''

D Returns 0

💡 Hint

Think about how redis-py handles keys that are not found.

When a key does not exist, r.get returns None, indicating absence of value without error.