Lambda vs regular functions in Python - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a lambda function that adds 5 to a number.

Python

add_five = lambda x: x [1] 5
print(add_five(10))

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

A-

B+

C*

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using '-' instead of '+' will subtract instead of add.

Using '*' or '/' will multiply or divide, not add.

The lambda function adds 5 to the input number using the + operator.

2fill in blank

medium

Complete the regular function to return the square of a number.

Python

def square(num):
    return num [1] num

print(square(4))

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

A/

B+

C-

D*

Attempts:

3 left

💡 Hint

Common Mistakes

Using '+' will add the number to itself, not square it.

Using '-' or '/' will not give the square.

The function returns the number multiplied by itself to get the square.

3fill in blank

hard

Fix the error in the lambda function that should multiply two numbers.

Python

multiply = lambda a, b: a [1] b
print(multiply(3, 7))

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

A*

B+

C-

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using '+' adds instead of multiplies.

Using '-' or '/' will not multiply.

The lambda function multiplies two numbers using the '*' operator.

4fill in blank

hard

Fill both blanks to create a dictionary comprehension that maps numbers to their squares using a lambda.

Python

square_func = lambda x: x [1] x
squares = {num: square_func(num) for num in range(1, 6) if num [2] 3}
print(squares)

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

A*

B>

C<

D+

Attempts:

3 left

💡 Hint

Common Mistakes

Using '+' in lambda adds instead of squares.

Using '<' includes numbers less than 3, not greater.

The lambda multiplies the number by itself to get the square. The comprehension includes numbers greater than 3.

5fill in blank

hard

Fill all three blanks to create a lambda that filters even numbers and returns their squares in a dictionary.

Python

is_even = lambda n: n [1] 2 == 0
square = lambda x: x [2] x
result = {num: square(num) for num in range(1, 11) if is_even(num) [3] True}
print(result)

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

A%

B*

C==

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '!=' instead of '==' changes the condition.

Using '+' instead of '*' does not square the number.

Using '/' instead of '%' does not check evenness.

The lambda 'is_even' checks if a number divided by 2 has remainder 0 using '%'. The 'square' lambda multiplies the number by itself. The dictionary comprehension includes numbers where 'is_even(num) == True'.

Practice

1. Which of the following best describes a lambda function in Python?

easy

A. A function defined using def that can have multiple statements.

B. A short, anonymous function defined with the lambda keyword.

C. A function that must always return None.

D. A function that can only be used inside classes.

Solution

1. Step 1: Understand lambda function definition

   A lambda function is defined using the lambda keyword and is anonymous (no name).

2. Step 2: Compare with regular functions

   Regular functions use def and can have multiple statements, unlike lambdas which are single expressions.

3. Final Answer:

   A short, anonymous function defined with the lambda keyword. -> Option B

4. Quick Check:

   Lambda = short anonymous function [OK]

Hint: Lambdas are short and nameless functions [OK]

Common Mistakes:

• Thinking lambdas can have multiple statements
• Confusing lambda with regular def functions
• Believing lambdas must return None

2. Which of the following is the correct syntax for a lambda function that adds 5 to its input?

easy

A. def add_five(x): return x + 5

B. lambda x x + 5

C. lambda x: x + 5

D. lambda (x): return x + 5

Solution

1. Step 1: Recall lambda syntax

   A lambda function is written as lambda parameters: expression without def or return.

2. Step 2: Check each option

   lambda x: x + 5 matches the correct syntax: lambda x: x + 5. Others have syntax errors or use def.

3. Final Answer:

   lambda x: x + 5 -> Option C

4. Quick Check:

   Lambda syntax = lambda params: expression [OK]

Hint: Lambda uses colon, no def or return [OK]

Common Mistakes:

• Including 'def' or 'return' in lambda
• Missing colon after parameters
• Using parentheses incorrectly

3. What is the output of the following code?

add = lambda x, y: x + y
def add_func(x, y):
    return x + y

print(add(3, 4))
print(add_func(3, 4))

medium

A. 7\n7

B. 34\n34

C. TypeError\nTypeError

D. None\nNone

Solution

1. Step 1: Understand lambda and regular function behavior

   Both add (lambda) and add_func (regular) add two numbers and return the sum.

2. Step 2: Evaluate the print statements

   Calling add(3, 4) and add_func(3, 4) both return 7, so output is two lines with 7.

3. Final Answer:

   7 7 -> Option A

4. Quick Check:

   Both add functions return sum = 7 [OK]

Hint: Both lambda and def return same result if logic matches [OK]

Common Mistakes:

• Thinking lambda returns string concatenation
• Confusing output with error messages
• Assuming lambda can't return values

4. Identify the error in this code snippet:

multiply = lambda x, y:
    x * y

print(multiply(2, 3))

medium

A. No error; output is 6

B. SyntaxError due to missing colon after lambda parameters

C. TypeError because lambda cannot take two arguments

D. IndentationError because lambda body is on new line

Solution

1. Step 1: Check lambda syntax rules

   Lambda functions must have their expression on the same line as the lambda keyword and parameters.

2. Step 2: Analyze the code structure

   The code places the expression x * y on the next line, causing an IndentationError.

3. Final Answer:

   IndentationError because lambda body is on new line -> Option D

4. Quick Check:

   Lambda body must be on same line [OK]

Hint: Lambda body must be on same line as parameters [OK]

Common Mistakes:

• Placing lambda body on next line
• Adding colon after lambda parameters
• Thinking lambda can't take multiple arguments

5. You want to sort a list of tuples by the second item using a function. Which is the best way to write the key function?

hard

A. list.sort(key=lambda t: t[1])

B. def get_second(t): return t[1]
list.sort(key=get_second(t))

C. list.sort(key=lambda t t[1])

D. list.sort(key=get_second())

Solution

1. Step 1: Understand sorting with key functions

   The key parameter expects a function that takes one argument and returns the value to sort by.

2. Step 2: Evaluate options for correctness and efficiency

   def get_second(t): return t[1] list.sort(key=get_second(t)) defines a regular function but incorrectly calls get_second(t) (causing NameError: 't' not defined). list.sort(key=lambda t: t[1]) uses a lambda inline, which is concise and common. list.sort(key=lambda t t[1]) has syntax error (missing colon). list.sort(key=get_second()) calls get_second() instead of passing the function.

3. Step 3: Choose best practice

   Using a lambda inline is best for simple, one-time use functions.

4. Final Answer:

   list.sort(key=lambda t: t[1]) -> Option A

5. Quick Check:

   Lambda inline for simple key function [OK]

Hint: Use lambda inline for simple sort keys [OK]

Common Mistakes:

• Forgetting colon in lambda
• Calling function instead of passing it
• Using multi-line def when lambda suffices