Lambda syntax and behavior in Python - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

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

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 subtraction or multiplication instead of addition.

Forgetting the operator between x and 5.

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

2fill in blank

medium

Complete the code to create a lambda function that returns True if a number is even.

Python

is_even = lambda n: n [1] 2 == 0
print(is_even(4))

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

A+

B%

C-

D*

Attempts:

3 left

💡 Hint

Common Mistakes

Using addition or multiplication instead of modulo.

Forgetting to compare the result to zero.

The modulo operator % gives the remainder. If remainder is 0 when divided by 2, the number is even.

3fill in blank

hard

Fix the error in the lambda function that should multiply input by 3.

Python

triple = lambda x: x [1] 3
print(triple(7))

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

A*

B+

C-

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using addition or subtraction instead of multiplication.

Using division which changes the value incorrectly.

The multiplication operator * is needed to multiply the input by 3.

4fill in blank

hard

Fill in the blank to create a lambda that returns True if a word's length is greater than 4.

Python

check_length = lambda word: len(word) [1] 4
print(check_length('hello'))

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

A>

B<

C==

D!=

Attempts:

3 left

💡 Hint

Common Mistakes

Using less than or equal operators instead of greater than.

Using equality operator which checks for exact length.

The operator > checks if the length is greater than 4.

5fill in blank

hard

Fill all three blanks to create a lambda that filters numbers greater than 10 and doubles them.

Python

result = list(filter(lambda x: x [1] 10, map(lambda x: x [2] [3], [5, 12, 7, 15])))
print(result)

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

A>

B*

C2

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using less than operator for filtering.

Using addition instead of multiplication for doubling.

Forgetting to provide the multiplier.

The lambda filters numbers greater than 10 using >, then doubles them by multiplying by 2.

Practice

1. What does a lambda function in Python do?

easy

A. Creates a small anonymous function with a single expression

B. Defines a class with methods

C. Declares a variable

D. Imports a module

Solution

1. Step 1: Understand lambda purpose

   A lambda function is a quick way to create a function without a name that returns the result of one expression.

2. Step 2: Compare options

   Only Creates a small anonymous function with a single expression describes this behavior correctly. Other options describe unrelated Python features.

3. Final Answer:

   Creates a small anonymous function with a single expression -> Option A

4. Quick Check:

   Lambda = anonymous single-expression function [OK]

Hint: Lambdas are short unnamed functions with one expression [OK]

Common Mistakes:

• Thinking lambda can have multiple statements
• Confusing lambda with class or variable definitions
• Assuming lambda needs a name

2. Which of the following is the correct syntax for a lambda function that adds two numbers x and y?

easy

A. lambda (x, y) { return x + y }

B. lambda x, y: x + y

C. def lambda(x, y): return x + y

D. lambda x, y => x + y

Solution

1. Step 1: Recall lambda syntax

   In Python, lambda syntax is: lambda parameters: expression

2. Step 2: Check each option

   lambda x, y: x + y matches correct syntax. Options B and D use other language styles. def lambda(x, y): return x + y wrongly uses def with lambda.

3. Final Answer:

   lambda x, y: x + y -> Option B

4. Quick Check:

   Correct lambda syntax = lambda params: expression [OK]

Hint: Remember: lambda params colon expression [OK]

Common Mistakes:

• Using parentheses around parameters in lambda
• Trying to use curly braces or return keyword
• Mixing lambda with def syntax

3. What is the output of this code?

func = lambda x: x * 2
print(func(5))

medium

A. 10

B. 25

C. SyntaxError

D. None

Solution

1. Step 1: Understand the lambda function

   The lambda takes input x and returns x multiplied by 2.

2. Step 2: Calculate func(5)

   func(5) = 5 * 2 = 10

3. Final Answer:

   10 -> Option A

4. Quick Check:

   5 * 2 = 10 [OK]

Hint: Multiply input by 2 as lambda defines [OK]

Common Mistakes:

• Confusing multiplication with addition
• Expecting syntax error due to lambda
• Thinking lambda returns None by default

4. Find the error in this lambda function:

double = lambda x: return x * 2
print(double(4))

medium

A. No error, code runs fine

B. Missing parentheses around x

C. Lambda cannot multiply numbers

D. Using 'return' inside lambda causes SyntaxError

Solution

1. Step 1: Check lambda syntax rules

   Lambdas cannot contain statements like 'return'; they only have an expression.

2. Step 2: Identify error in code

   The code uses 'return' inside lambda, which is invalid and causes SyntaxError.

3. Final Answer:

   Using 'return' inside lambda causes SyntaxError -> Option D

4. Quick Check:

   Lambda disallows 'return' keyword [OK]

Hint: Lambdas never use 'return' keyword [OK]

Common Mistakes:

• Adding 'return' inside lambda
• Thinking parentheses are mandatory around parameters
• Believing lambda can't do math operations

5. You want to create a list of squares for numbers 1 to 5 using a lambda inside map. Which code correctly does this?

hard

A. list(map(lambda x: x*2, range(1, 5)))

B. map(lambda x: x**2, [1, 2, 3, 4, 5])

C. list(map(lambda x: x**2, range(1, 6)))

D. list(map(lambda x: x**2, range(5)))

Solution

1. Step 1: Understand the goal

   Create squares of numbers 1 to 5 inclusive, so numbers are 1,2,3,4,5.

2. Step 2: Check each option

   list(map(lambda x: x**2, range(1, 6))) uses range(1,6) which includes 1 to 5 and squares each number correctly.
   list(map(lambda x: x*2, range(1, 5))) doubles numbers and uses range(1,5) which excludes 5.
   map(lambda x: x**2, [1, 2, 3, 4, 5]) returns a map object, not a list.
   list(map(lambda x: x**2, range(5))) uses range(5) which is 0 to 4, not 1 to 5.

3. Final Answer:

   list(map(lambda x: x**2, range(1, 6))) -> Option C

4. Quick Check:

   Squares 1-5 with map and lambda [OK]

Hint: Use range(1,6) and lambda x: x**2 inside list(map()) [OK]

Common Mistakes:

• Using range(5) which starts at 0
• Forgetting to convert map to list
• Using wrong lambda expression like x*2