Deserialization in Kafka - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Kafka deserialization code?

Consider the following Kafka consumer code snippet that deserializes messages from a topic. What will be printed when a message with value {"name":"Alice","age":30} is consumed?

Kafka

from kafka import KafkaConsumer
import json

consumer = KafkaConsumer(
    'users',
    bootstrap_servers=['localhost:9092'],
    value_deserializer=lambda m: json.loads(m.decode('utf-8'))
)

for message in consumer:
    print(message.value['name'])
    break

A {'name': 'Alice', 'age': 30}

B Alice

C b'{"name":"Alice","age":30}'

D None

💡 Hint

Think about what the value_deserializer does to the message bytes.

The value_deserializer converts the byte string into a Python dictionary. Accessing message.value['name'] prints the string Alice.

🧠 Conceptual

intermediate

Which deserializer is appropriate for Avro data in Kafka?

You receive Kafka messages encoded in Avro format. Which deserializer should you use to correctly convert the message bytes into usable data?

A A JSON deserializer that decodes UTF-8 strings

B A plain string deserializer that converts bytes to strings

C An Avro deserializer that uses the schema registry to decode bytes

D A protobuf deserializer that parses protobuf messages

💡 Hint

Avro data requires schema information to deserialize properly.

Avro data is binary and requires a deserializer that can use the schema registry to interpret the bytes correctly.

🔧 Debug

advanced

Why does this Kafka consumer raise a deserialization error?

Examine the following Kafka consumer code. It raises a deserialization error when consuming messages. What is the cause?

Kafka

from kafka import KafkaConsumer
import json

consumer = KafkaConsumer(
    'events',
    bootstrap_servers=['localhost:9092'],
    value_deserializer=lambda m: m.decode('utf-8')
)

for message in consumer:
    data = json.loads(message.value)
    print(data['event'])

A The <code>value_deserializer</code> decodes bytes to string, so calling <code>json.loads</code> again on string causes error

B The <code>value_deserializer</code> returns a string, but <code>json.loads</code> expects bytes

C The topic name is incorrect, causing deserialization failure

D The bootstrap server address is invalid

💡 Hint

Check the data type passed to json.loads.

The value_deserializer already decodes bytes to string. Calling json.loads again on a string causes a TypeError because json.loads expects a string, but the code tries to decode twice.

📝 Syntax

advanced

Identify the syntax error in this Kafka deserializer setup

Which option contains a syntax error in the Kafka consumer deserializer configuration?

A value_deserializer=lambda m: None if m is None else json.loads(m.decode('utf-8'))

B value_deserializer=lambda m: json.loads(m.decode('utf-8'))

C value_deserializer=lambda m: json.loads(m.decode('utf-8')) if m else None

D value_deserializer=lambda m: json.loads(m.decode('utf-8')

💡 Hint

Look carefully at the parentheses.

Option D is missing a closing parenthesis for json.loads, causing a syntax error.

🚀 Application

expert

How many items are in the resulting dictionary after deserialization?

A Kafka message value is a JSON string: {"id":123,"tags":["red","blue"],"active":true}. After deserializing with json.loads, how many top-level keys does the resulting Python dictionary have?

Kafka

import json

message_value = b'{"id":123,"tags":["red","blue"],"active":true}'
data = json.loads(message_value.decode('utf-8'))

result = len(data)

A 3

B 1

C 2

D 4

💡 Hint

Count the keys at the top level of the JSON object.

The JSON object has three keys: id, tags, and active. So the length of the dictionary is 3.