Set creation in Python - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of set creation with duplicates

What is the output of this Python code?

my_set = {1, 2, 2, 3, 4, 4, 4}
print(my_set)

Python

my_set = {1, 2, 2, 3, 4, 4, 4}
print(my_set)

A {1, 2, 3, 4}

B {1, 2, 2, 3, 4, 4, 4}

C [1, 2, 3, 4]

D (1, 2, 3, 4)

💡 Hint

Remember that sets do not keep duplicates.

Sets automatically remove duplicate values, so only unique elements remain.

❓ Predict Output

intermediate

Creating a set from a list

What will be printed by this code?

my_list = [5, 6, 7, 5, 6]
my_set = set(my_list)
print(my_set)

Python

my_list = [5, 6, 7, 5, 6]
my_set = set(my_list)
print(my_set)

A (5, 6, 7)

B [5, 6, 7, 5, 6]

C {5, 6, 7}

D {5, 6, 7, 5, 6}

💡 Hint

Converting a list to a set removes duplicates.

The set constructor removes duplicates and keeps unique elements only.

❓ Predict Output

advanced

Set comprehension with condition

What is the output of this code?

result = {x * x for x in range(5) if x % 2 == 0}
print(result)

Python

result = {x * x for x in range(5) if x % 2 == 0}
print(result)

A {0, 2, 4, 6, 8}

B {1, 9, 25}

C {0, 1, 4, 9, 16}

D {0, 4, 16}

💡 Hint

Only even numbers from 0 to 4 are squared.

The comprehension squares only even numbers: 0, 2, 4 → 0, 4, 16.

❓ Predict Output

advanced

Set creation with mutable elements

What error does this code raise?

my_set = {1, 2, [3, 4]}

Python

my_set = {1, 2, [3, 4]}

A TypeError

B SyntaxError

C ValueError

D No error, set created

💡 Hint

Sets cannot contain mutable elements like lists.

Lists are mutable and cannot be added to sets, causing a TypeError.

🧠 Conceptual

expert

Number of items in a set after complex creation

How many items are in the set after running this code?

data = [1, 2, 2, 3, 4, 4, 5]
result = {x for x in data if x % 2 != 0}
print(len(result))

Python

data = [1, 2, 2, 3, 4, 4, 5]
result = {x for x in data if x % 2 != 0}
print(len(result))

A 7

B 3

C 4

D 5

💡 Hint

Count unique odd numbers in the list.

Odd numbers are 1, 3, 5. They are unique, so length is 3.

Practice

1. Which of the following is the correct way to create a set with the elements 1, 2, and 3 in Python?

easy

A. (1, 2, 3)

B. [1, 2, 3]

C. {1, 2, 3}

D. set[1, 2, 3]

Solution

1. Step 1: Understand set creation syntax

   Sets are created using curly braces with comma-separated values or the set() function.

2. Step 2: Identify correct syntax for set with elements

   {1, 2, 3} correctly creates a set with elements 1, 2, and 3.

3. Final Answer:

   {1, 2, 3} -> Option C

4. Quick Check:

   Curly braces with values = set [OK]

Hint: Use curly braces with commas for sets, not brackets [OK]

Common Mistakes:

• Using square brackets creates a list, not a set
• Using parentheses creates a tuple, not a set
• Using set[] is invalid syntax

2. What is the correct way to create an empty set in Python?

easy

A. set()

B. {}

C. []

D. empty_set()

Solution

1. Step 1: Recognize empty set syntax

   Using {} creates an empty dictionary, not a set.

2. Step 2: Use the set() function for empty sets

   set() correctly creates an empty set.

3. Final Answer:

   set() -> Option A

4. Quick Check:

   Empty set = set() function [OK]

Hint: Empty sets need set(), not curly braces [OK]

Common Mistakes:

• Using {} creates an empty dictionary, not a set
• Using [] creates an empty list
• Using undefined functions like empty_set()

3. What will be the output of the following code?

my_set = {1, 2, 2, 3, 4, 4}
print(my_set)

medium

A. {1, 2, 2, 3, 4, 4}

B. [1, 2, 3, 4]

C. (1, 2, 3, 4)

D. {1, 2, 3, 4}

Solution

1. Step 1: Understand set uniqueness property

   Sets automatically remove duplicate elements, so repeated values appear only once.

2. Step 2: Apply uniqueness to given elements

   Duplicates 2 and 4 are removed, leaving {1, 2, 3, 4}.

3. Final Answer:

   {1, 2, 3, 4} -> Option D

4. Quick Check:

   Sets remove duplicates = {1, 2, 3, 4} [OK]

Hint: Sets keep unique items only, duplicates vanish [OK]

Common Mistakes:

• Expecting duplicates to remain in the set
• Confusing set output with list or tuple syntax
• Thinking sets preserve order

4. Identify the error in the following code snippet:

my_set = set{1, 2, 3}
print(my_set)

medium

A. SyntaxError due to incorrect set creation syntax

B. Prints {1, 2, 3} correctly

C. TypeError because set() expects a list

D. NameError because set is not defined

Solution

1. Step 1: Check set creation syntax

   The correct way to create a set using the function is set() with parentheses, not curly braces.

2. Step 2: Identify syntax error

   set{1, 2, 3} is invalid syntax and causes a SyntaxError.

3. Final Answer:

   SyntaxError due to incorrect set creation syntax -> Option A

4. Quick Check:

   Use set() with parentheses, not braces [OK]

Hint: Use parentheses with set(), not curly braces [OK]

Common Mistakes:

• Using curly braces after set instead of parentheses
• Confusing set() with dictionary syntax
• Assuming set is undefined

5. Given the list nums = [1, 2, 2, 3, 4, 4, 5], which code snippet correctly creates a set of unique elements from this list?

hard

A. unique_nums = {nums}

B. unique_nums = set(nums)

C. unique_nums = list(set(nums))

D. unique_nums = {1, 2, 3, 4, 5}

Solution

1. Step 1: Understand how to convert list to set

   The set() function can take an iterable like a list and return a set of unique elements.

2. Step 2: Analyze each option

   unique_nums = {nums} creates a set with the entire list as one element (invalid). unique_nums = set(nums) correctly converts the list to a set. unique_nums = list(set(nums)) converts to set then back to list, which is not a set. unique_nums = {1, 2, 3, 4, 5} manually writes the set but is not dynamic.

3. Final Answer:

   unique_nums = set(nums) -> Option B

4. Quick Check:

   Use set() on list to get unique elements [OK]

Hint: Use set() on list to get unique items fast [OK]

Common Mistakes:

• Trying to put list inside curly braces directly
• Converting set back to list when set is needed
• Hardcoding values instead of using the list variable