Lambda function concept in AWS - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to define a basic AWS Lambda function handler in Python.

AWS

def lambda_handler(event, context):
    return [1]

Drag options to blanks, or click blank then click option'

Aprint("Hello")

B"Hello from Lambda!"

Cevent + context

DNone

Attempts:

3 left

💡 Hint

Common Mistakes

Using print instead of return

Returning None which means no response

The Lambda handler must return a value, here a simple greeting string.

2fill in blank

medium

Complete the code to access the 'name' key from the event dictionary in the Lambda function.

AWS

def lambda_handler(event, context):
    name = event[1]"name"
    return f"Hello, {name}!"

Drag options to blanks, or click blank then click option'

A["name"]

B("name")

C.name

D{'name'}

Attempts:

3 left

💡 Hint

Common Mistakes

Using parentheses or dot notation which are invalid for dict access

Event is a dictionary; use square brackets to access keys.

3fill in blank

hard

Fix the error in the Lambda function code to correctly handle missing 'age' key in event.

AWS

def lambda_handler(event, context):
    age = event.get([1], 0)
    return f"Age is {age}"

Drag options to blanks, or click blank then click option'

Aage

Bevent

C0

D"age"

Attempts:

3 left

💡 Hint

Common Mistakes

Using variable name without quotes

Passing wrong type as key

The key must be a string in quotes when using dict.get().

4fill in blank

hard

Fill both blanks to create a Lambda function that returns the square of a number passed in event.

AWS

def lambda_handler(event, context):
    number = event[1]"number"
    result = number [2] 2
    return result

Drag options to blanks, or click blank then click option'

A["number"]

B**

C*

D("number")

Attempts:

3 left

💡 Hint

Common Mistakes

Using * instead of ** for square

Using parentheses instead of brackets for dict access

Access the number with event["number"] and use ** for exponentiation.

5fill in blank

hard

Fill all three blanks to create a Lambda function that returns a dictionary with the original number, its square, and a greeting message.

AWS

def lambda_handler(event, context):
    num = event[1]"num"
    square = num [2] 2
    return [3]

Drag options to blanks, or click blank then click option'

A["num"]

B**

C{"number": num, "square": square, "message": "Hello!"}

D("num")

Attempts:

3 left

💡 Hint

Common Mistakes

Using parentheses instead of brackets

Using * instead of **

Returning a string instead of a dictionary

Access 'num' with event["num"], square with **, and return a dictionary with keys and values.

Practice

1. What is the main purpose of an AWS Lambda function?

easy

A. To store large amounts of data

B. To run code automatically without managing servers

C. To create virtual machines

D. To manage user permissions

Solution

1. Step 1: Understand Lambda's role

   AWS Lambda runs your code without needing you to manage servers.

2. Step 2: Compare options

   Options A, C, and D describe other AWS services, not Lambda.

3. Final Answer:

   To run code automatically without managing servers -> Option B

4. Quick Check:

   Lambda = serverless code execution [OK]

Hint: Lambda runs code without servers, not storage or VMs [OK]

Common Mistakes:

• Confusing Lambda with storage services
• Thinking Lambda creates virtual machines
• Assuming Lambda manages user permissions

2. Which of the following is the correct way to define a simple AWS Lambda function handler in Python?

easy

A. lambda handler(event): print('Hello World')

B. function handler(event) { return 'Hello World'; }

C. def handler(event, context): return 'Hello World'

D. def handler(): print('Hello World')

Solution

1. Step 1: Identify correct Python Lambda handler syntax

   Lambda handlers in Python must accept two parameters: event and context.

2. Step 2: Check each option

   def handler(event, context): return 'Hello World' correctly defines a Python function with event and context parameters and returns a string. function handler(event) { return 'Hello World'; } is JavaScript syntax. lambda handler(event): print('Hello World') misuses lambda keyword. def handler(): print('Hello World') lacks required parameters.

3. Final Answer:

   def handler(event, context): return 'Hello World' -> Option C

4. Quick Check:

   Python Lambda handler needs event and context [OK]

Hint: Python Lambda handlers always have (event, context) parameters [OK]

Common Mistakes:

• Using JavaScript syntax in Python Lambda
• Omitting event or context parameters
• Misusing lambda keyword for handler

3. Given this AWS Lambda Python code:

def handler(event, context):
    name = event.get('name', 'Guest')
    return f"Hello, {name}!"

What will be the output if the event is {}?

medium

A. "Hello, Guest!"

B. "Hello, None!"

C. Error: 'name' key missing

D. "Hello, !"

Solution

1. Step 1: Analyze event input and code behavior

   The event is an empty dictionary, so event.get('name', 'Guest') returns the default 'Guest'.

2. Step 2: Determine return value

   The function returns the string "Hello, Guest!" because 'name' is not in event.

3. Final Answer:

   "Hello, Guest!" -> Option A

4. Quick Check:

   Missing key uses default value 'Guest' [OK]

Hint: event.get with default returns default if key missing [OK]

Common Mistakes:

• Assuming missing key causes error
• Thinking None is returned instead of default
• Ignoring default value in get()

4. You wrote this AWS Lambda function in Python:

def handler(event, context):
    return event['message']

When triggered with event {}, it throws a KeyError. How can you fix it?

medium

A. Use event.get('message', 'No message') instead of event['message']

B. Remove the return statement

C. Add a print statement before return

D. Change function name to lambda_handler

Solution

1. Step 1: Identify cause of KeyError

   Accessing event['message'] when 'message' key is missing causes KeyError.

2. Step 2: Use safe access method

   Replacing event['message'] with event.get('message', 'No message') avoids error by providing default.

3. Final Answer:

   Use event.get('message', 'No message') instead of event['message'] -> Option A

4. Quick Check:

   Use get() to avoid KeyError on missing keys [OK]

Hint: Use get() with default to prevent KeyError [OK]

Common Mistakes:

• Ignoring missing key causes error
• Thinking print fixes KeyError
• Assuming function name affects key access

5. You want an AWS Lambda function to process image uploads to S3 and resize them. Which combination of AWS services and Lambda features is best suited for this task?

hard

A. Use Lambda to create EC2 instances that resize images

B. Run Lambda on a schedule to scan S3 and resize images manually

C. Upload images directly to Lambda storage for resizing

D. Use S3 event trigger on object creation to invoke Lambda, which resizes images and saves back to S3

Solution

1. Step 1: Understand event-driven processing

   S3 can trigger Lambda automatically when new objects are created, ideal for immediate processing.

2. Step 2: Evaluate options for image resizing

   Use S3 event trigger on object creation to invoke Lambda, which resizes images and saves back to S3 uses S3 event triggers and Lambda to resize and save images back to S3, which is efficient and serverless. Run Lambda on a schedule to scan S3 and resize images manually delays processing and requires scanning. Use Lambda to create EC2 instances that resize images misuses Lambda to create servers. Upload images directly to Lambda storage for resizing is invalid as Lambda has no persistent storage for uploads.

3. Final Answer:

   Use S3 event trigger on object creation to invoke Lambda, which resizes images and saves back to S3 -> Option D

4. Quick Check:

   S3 event triggers + Lambda = best for image processing [OK]

Hint: Use S3 event triggers to run Lambda on uploads [OK]

Common Mistakes:

• Thinking Lambda can store files persistently
• Using scheduled scans instead of event triggers
• Misusing Lambda to create servers