Python consumer in Kafka - Mini Project: Build & Apply

Python Kafka Consumer

📖 Scenario: You are building a simple Python program that listens to messages from a Kafka topic. Kafka is like a message bus where different programs can send and receive messages. Your program will act as a consumer that reads messages from a specific topic.

🎯 Goal: Create a Python Kafka consumer that connects to a Kafka server, subscribes to a topic named test-topic, and prints out messages it receives.

📋 What You'll Learn

Create a Kafka consumer connected to localhost:9092

Subscribe to the topic test-topic

Poll messages from the topic

Print each received message's value

💡 Why This Matters

🌍 Real World

Kafka consumers are used in real applications to process streams of data like logs, user activity, or sensor data in real time.

💼 Career

Understanding Kafka consumers is important for roles in data engineering, backend development, and real-time data processing.

1

Set up Kafka consumer configuration

Create a dictionary called conf with these exact entries: 'bootstrap.servers': 'localhost:9092', 'group.id': 'mygroup', and 'auto.offset.reset': 'earliest'.

Kafka

# Your code here

Hint

This dictionary holds the settings needed to connect to Kafka.

2

Create the Kafka consumer

Import Consumer from confluent_kafka and create a variable called consumer by passing the conf dictionary to Consumer(conf).

Kafka

conf = {
    'bootstrap.servers': 'localhost:9092',
    'group.id': 'mygroup',
    'auto.offset.reset': 'earliest'
}

# Your code here

Hint

Use the Consumer class to create a consumer object with the configuration.

3

Subscribe to the topic

Use the consumer.subscribe() method to subscribe to a list containing the single topic 'test-topic'.

Kafka

from confluent_kafka import Consumer

conf = {
    'bootstrap.servers': 'localhost:9092',
    'group.id': 'mygroup',
    'auto.offset.reset': 'earliest'
}

consumer = Consumer(conf)

# Your code here

Hint

Subscribe to the topic by passing a list with the topic name.

4

Poll and print messages

Write a while True loop that polls messages from consumer.poll(1.0). If a message is received and has no error, print its value decoded as UTF-8. Break the loop after printing one message.

Kafka

from confluent_kafka import Consumer

conf = {
    'bootstrap.servers': 'localhost:9092',
    'group.id': 'mygroup',
    'auto.offset.reset': 'earliest'
}

consumer = Consumer(conf)

consumer.subscribe(['test-topic'])

# Your code here

Hint

This loop waits for a message, checks for errors, prints the message text, then stops.

Practice

1.

What is the main purpose of a Python Kafka consumer?

easy

A. To create Kafka topics automatically

B. To send messages to Kafka topics

C. To read messages from Kafka topics and process them in Python

D. To monitor Kafka server health

Solution

1. Step 1: Understand Kafka consumer role

   A Kafka consumer reads data from Kafka topics to use in applications.

2. Step 2: Differentiate from producer

   Producers send messages, consumers read them. Monitoring and topic creation are separate tasks.

3. Final Answer:

   To read messages from Kafka topics and process them in Python -> Option C

4. Quick Check:

   Consumer = reads messages [OK]

Hint: Consumers read, producers write messages in Kafka [OK]

Common Mistakes:

• Confusing consumer with producer
• Thinking consumer creates topics
• Assuming consumer monitors server

2.

Which of the following is the correct way to create a KafkaConsumer in Python to read from topic my_topic on localhost?

from kafka import KafkaConsumer
consumer = KafkaConsumer(_____)

easy

A. my_topic, bootstrap_servers='localhost:9092'

B. "my_topic", bootstrap='localhost:9092'

C. "my_topic", servers='localhost:9092'

D. "my_topic", bootstrap_servers='localhost:9092'

Solution

1. Step 1: Check KafkaConsumer parameters

   KafkaConsumer expects topic name as string and bootstrap_servers keyword argument.

2. Step 2: Identify correct syntax

   "my_topic", bootstrap_servers='localhost:9092' uses correct string for topic and correct keyword bootstrap_servers with proper value.

3. Final Answer:

   "my_topic", bootstrap_servers='localhost:9092' -> Option D

4. Quick Check:

   Correct syntax uses bootstrap_servers keyword [OK]

Hint: Use bootstrap_servers='host:port' exactly [OK]

Common Mistakes:

• Omitting quotes around topic name
• Using wrong keyword like servers or bootstrap
• Passing topic name without quotes

3.

What will be the output of this code snippet if the Kafka topic test has one message with value b'hello'?

from kafka import KafkaConsumer
consumer = KafkaConsumer("test", bootstrap_servers='localhost:9092', auto_offset_reset='earliest', group_id='group1')
for msg in consumer:
    print(msg.value.decode('utf-8'))
    break

medium

A. hello

B. b'hello'

C. msg.value

D. Error: decode method not found

Solution

1. Step 1: Understand message value type

   Kafka messages are bytes, so msg.value is b'hello'.

2. Step 2: Decode bytes to string

   Calling decode('utf-8') converts b'hello' to 'hello' string, which is printed.

3. Final Answer:

   hello -> Option A

4. Quick Check:

   Decoded bytes print string [OK]

Hint: Decode bytes with decode('utf-8') to get string [OK]

Common Mistakes:

• Printing raw bytes without decoding
• Trying to decode string instead of bytes
• Expecting b'hello' printed as string

4.

Identify the error in this Kafka consumer code snippet:

from kafka import KafkaConsumer
consumer = KafkaConsumer('topic1', bootstrap_servers='localhost:9092')
for message in consumer:
    print(message.value.decode())
consumer.close()

medium

A. decode() requires an encoding argument

B. The consumer.close() is called outside the loop and never reached

C. Missing group_id parameter in KafkaConsumer

D. The for loop should use consumer.poll() instead

Solution

1. Step 1: Analyze loop and close call

   The for loop on consumer is infinite; code never reaches consumer.close() after loop.

2. Step 2: Understand consumer.close() usage

   To close consumer properly, loop must break or use context manager; otherwise close() is unreachable.

3. Final Answer:

   The consumer.close() is called outside the loop and never reached -> Option B

4. Quick Check:

   Infinite loop blocks close() call [OK]

Hint: Infinite loops prevent code after them from running [OK]

Common Mistakes:

• Assuming decode() needs encoding argument
• Thinking group_id is mandatory
• Confusing poll() with iteration

5.

You want to consume messages from two Kafka topics topicA and topicB using one Python KafkaConsumer instance. Which code snippet correctly sets this up?

from kafka import KafkaConsumer
consumer = KafkaConsumer(_____)
for msg in consumer:
    print(f"Topic: {msg.topic}, Message: {msg.value.decode()}")

hard

A. ["topicA", "topicB"], bootstrap_servers='localhost:9092', auto_offset_reset='earliest', group_id='group1'

B. "topicA,topicB", bootstrap_servers='localhost:9092', group_id='group1'

C. "topicA" and "topicB", bootstrap_servers='localhost:9092'

D. "topicA"; "topicB", bootstrap_servers='localhost:9092', group_id='group1'

Solution

1. Step 1: Check how to subscribe to multiple topics

   KafkaConsumer accepts a list of topic names to subscribe to multiple topics.

2. Step 2: Verify correct syntax for multiple topics

   ["topicA", "topicB"], bootstrap_servers='localhost:9092', auto_offset_reset='earliest', group_id='group1' correctly passes a list ["topicA", "topicB"] and required parameters.

3. Final Answer:

   ["topicA", "topicB"], bootstrap_servers='localhost:9092', auto_offset_reset='earliest', group_id='group1' -> Option A

4. Quick Check:

   List of topics subscribes to multiple topics [OK]

Hint: Use list of topic names to consume multiple topics [OK]

Common Mistakes:

• Passing topics as comma-separated string
• Using logical operators like and or ; between topics
• Omitting group_id for consumer group