Redis with Python (redis-py) - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is Redis in simple terms?

Redis is like a super-fast notebook where you can quickly save and find information while your program is running.

beginner

How do you connect to a Redis server using redis-py?

You create a Redis client in Python by calling redis.Redis(host='localhost', port=6379) which connects your program to the Redis server.

beginner

What Python command sets a key-value pair in Redis?

Use client.set('key', 'value') to save a value under a key in Redis.

beginner

How do you get a value from Redis using redis-py?

Use client.get('key') to retrieve the value stored under that key. It returns bytes, so you often decode it to a string.

beginner

Why is Redis useful for Python programs?

Redis helps Python programs by storing data quickly in memory, making tasks like caching, counting, or messaging very fast and efficient.

Which Python library do you use to work with Redis?

A numpy

B pandas

C redis-py

D matplotlib

The redis-py library is the official Python client to interact with Redis.

What does client.set('name', 'Alice') do in redis-py?

A Deletes the key 'name'

B Stores the value 'Alice' under the key 'name'

C Retrieves the value of 'name'

D Connects to Redis server

The set command saves the value 'Alice' under the key 'name' in Redis.

What type of data does client.get('key') return?

A String

B Integer

C List

D Bytes

Redis returns data as bytes, so you often decode it to string in Python.

Which port does Redis use by default?

A 6379

B 5432

C 8080

D 3306

Redis listens on port 6379 by default.

Why might you use Redis in a Python app?

A To speed up data access by storing data in memory

B To store data on disk permanently

C To create graphics

D To write web pages

Redis stores data in memory, making data access very fast, which helps speed up Python apps.

Explain how to connect to Redis and set a key-value pair using redis-py.

Think about how you start talking to Redis and then save something.

Describe why Redis is helpful for Python programs and give one example use case.

Imagine Redis as a fast notebook for your program.

Practice

1. What does the set() method do in redis-py?

easy

A. Lists all keys stored in Redis

B. Retrieves a value by key from Redis

C. Deletes a key from Redis

D. Stores a value with a specified key in Redis

Solution

1. Step 1: Understand the purpose of set()

   The set() method is used to save data in Redis by associating a value with a key.

2. Step 2: Compare with other methods

   get() retrieves data, delete() removes keys, and keys() lists keys, so they do not store data.

3. Final Answer:

   Stores a value with a specified key in Redis -> Option D

4. Quick Check:

   set() means store data [OK]

Hint: Remember: set = save data, get = retrieve data [OK]

Common Mistakes:

• Confusing set() with get()
• Thinking set() deletes keys
• Assuming set() lists keys

2. Which of the following is the correct syntax to get a value for key 'name' using redis-py?

easy

A. r.get('name')

B. r.get(name)

C. r.get['name']

D. r.get{name}

Solution

1. Step 1: Identify correct method call syntax

   In Python, method calls use parentheses with arguments inside, so r.get('name') is correct.

2. Step 2: Check argument format

   The key must be a string, so it needs quotes. Options A, B, and D have syntax errors or missing quotes.

3. Final Answer:

   r.get('name') -> Option A

4. Quick Check:

   Method call with parentheses and string key [OK]

Hint: Use parentheses and quotes for string keys in method calls [OK]

Common Mistakes:

• Omitting quotes around string keys
• Using square brackets instead of parentheses
• Using curly braces instead of parentheses

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

import redis
r = redis.Redis()
r.set('color', 'blue')
value = r.get('color')
print(value)

medium

A. blue

B. b'blue'

C. None

D. Error

Solution

1. Step 1: Understand Redis returns bytes

   The get() method returns the value as bytes, so value is b'blue'.

2. Step 2: Print output

   Printing value shows the bytes literal b'blue', not the decoded string.

3. Final Answer:

   b'blue' -> Option B

4. Quick Check:

   Redis returns bytes, so output shows b'...' [OK]

Hint: Remember: Redis get returns bytes, not decoded string [OK]

Common Mistakes:

• Expecting a plain string without decoding
• Assuming None if key exists
• Thinking code raises error

4. Identify the error in this code snippet:

import redis
r = redis.Redis()
r.set('age', 30)
age = r.get('age')
print(age)

medium

A. get() returns bytes, need decoding

B. Cannot store integer directly with set()

C. Missing Redis server connection parameters

D. Syntax error in print statement

Solution

1. Step 1: Check data storage

   Redis-py converts integers to strings automatically, so storing 30 is valid.

2. Step 2: Check retrieval and printing

   get() returns bytes, so printing age shows bytes, not a readable string or integer. Decoding is needed.

3. Final Answer:

   get() returns bytes, need decoding -> Option A

4. Quick Check:

   Decode bytes after get() to read value [OK]

Hint: Always decode bytes from get() before printing [OK]

Common Mistakes:

• Thinking set() rejects integers
• Ignoring bytes return type from get()
• Assuming print syntax error

5. You want to store user info as a dictionary in Redis using redis-py. Which approach correctly saves and retrieves the dictionary?

hard

A. Store dictionary as string with set() and retrieve with get() without decoding

B. Directly use set() with the dictionary and get() to retrieve

C. Use set() with json.dumps() to save and json.loads() after get()

D. Use hmset() to save and hgetall() to retrieve

Solution

1. Step 1: Understand Redis stores strings/bytes

   Redis cannot store Python dicts directly; they must be converted to strings.

2. Step 2: Use JSON to serialize and deserialize

   Using json.dumps() converts dict to string for set(), and json.loads() converts back after get().

3. Step 3: Evaluate other options

   hmset() is deprecated; direct dict storage fails; storing string without decoding causes errors.

4. Final Answer:

   Use set() with json.dumps() and json.loads() after get() -> Option C

5. Quick Check:

   Serialize dict to string before storing, deserialize after retrieval [OK]

Hint: Serialize dict with JSON before set(), deserialize after get() [OK]

Common Mistakes:

• Trying to store dict directly
• Using deprecated hmset() method
• Not decoding bytes before json.loads()