Python consumer in Kafka - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Kafka consumer code snippet?

Consider the following Python Kafka consumer code using confluent_kafka. What will be printed?

Kafka

from confluent_kafka import Consumer

conf = {'bootstrap.servers': 'localhost:9092', 'group.id': 'testgroup', 'auto.offset.reset': 'earliest'}
consumer = Consumer(conf)
consumer.subscribe(['mytopic'])

msg = consumer.poll(timeout=1.0)
if msg is None:
    print('No message received')
elif msg.error():
    print(f'Error: {msg.error()}')
else:
    print(f'Received message: {msg.value().decode("utf-8")}')
consumer.close()

A Error: KafkaError{code=_UNKNOWN_TOPIC_OR_PART}

B Received message: <message content>

C No message received

D Raises a TypeError

💡 Hint

If the topic has no messages or Kafka is not running, poll returns None.

The poll method waits for a message. If none arrives within 1 second, it returns None. So the code prints 'No message received'.

❓ Predict Output

intermediate

What does this Kafka consumer print when a message with value 'hello' is received?

Given this code snippet, what will be printed if a message with value b'hello' is received?

Kafka

from confluent_kafka import Consumer

conf = {'bootstrap.servers': 'localhost:9092', 'group.id': 'grp1', 'auto.offset.reset': 'earliest'}
consumer = Consumer(conf)
consumer.subscribe(['topic1'])

msg = consumer.poll(timeout=2.0)
if msg and not msg.error():
    print(f'Message: {msg.value().decode()}')
else:
    print('No valid message')
consumer.close()

A Message: b'hello'

B Raises a UnicodeDecodeError

C No valid message

D Message: hello

💡 Hint

Message values are bytes and need decoding to strings.

The message value is bytes b'hello'. Decoding it with decode() converts it to string 'hello'.

🧠 Conceptual

advanced

Which error will this Kafka consumer code raise?

What error will this code raise when run?

Kafka

from confluent_kafka import Consumer

conf = {'bootstrap.servers': 'localhost:9092', 'group.id': 'grp2'}
consumer = Consumer(conf)
consumer.subscribe(['topic2'])

msg = consumer.poll(timeout=1.0)
print(msg.value().decode('utf-8'))
consumer.close()

A No error, prints message value

B AttributeError: 'NoneType' object has no attribute 'value'

C UnicodeDecodeError

D KafkaException

💡 Hint

If poll returns None, calling value() causes an error.

If no message is received, poll returns None. Calling value() on None raises AttributeError.

❓ Predict Output

advanced

What is the output of this Kafka consumer loop?

What will this code print if the topic has three messages with values 'one', 'two', 'three'?

Kafka

from confluent_kafka import Consumer

conf = {'bootstrap.servers': 'localhost:9092', 'group.id': 'grp3', 'auto.offset.reset': 'earliest'}
consumer = Consumer(conf)
consumer.subscribe(['topic3'])

count = 0
while count < 3:
    msg = consumer.poll(timeout=1.0)
    if msg and not msg.error():
        print(msg.value().decode())
        count += 1
consumer.close()

A one\ntwo\nthree

B three\ntwo\none

C No output

D Raises a RuntimeError

💡 Hint

The consumer reads messages in order from the topic.

The consumer polls and prints each message in the order they were produced: 'one', 'two', 'three'.

🔧 Debug

expert

Why does this Kafka consumer code hang indefinitely?

Given this code, why does it never exit the loop?

Kafka

from confluent_kafka import Consumer

conf = {'bootstrap.servers': 'localhost:9092', 'group.id': 'grp4', 'auto.offset.reset': 'latest'}
consumer = Consumer(conf)
consumer.subscribe(['topic4'])

while True:
    msg = consumer.poll(timeout=0.5)
    if msg is None:
        continue
    if msg.error():
        print(f'Error: {msg.error()}')
        break
    print(msg.value().decode())
consumer.close()

A Because 'auto.offset.reset' is 'latest' and no new messages arrive, poll returns None forever

B Because the loop condition is always True without a break on valid messages

C Because consumer.close() is never called inside the loop

D Because poll timeout is too short causing infinite retries

💡 Hint

Think about what happens if the consumer starts after messages were produced and 'auto.offset.reset' is 'latest'.

With 'auto.offset.reset' set to 'latest', the consumer waits for new messages after the current end. If no new messages arrive, poll returns None repeatedly, causing the loop to continue forever.