Why sets are used in Python - See It in Action

Why sets are used

📖 Scenario: Imagine you have a list of fruits you bought from the market, but some fruits are repeated. You want to find out which unique fruits you have without any duplicates.

🎯 Goal: Learn how to use a set in Python to find unique items from a list and understand why sets are useful.

📋 What You'll Learn

Create a list called fruits with some repeated fruit names

Create a set called unique_fruits from the fruits list

Print the unique_fruits set to see only unique fruit names

💡 Why This Matters

🌍 Real World

Sets help when you want to find unique things like unique customers, unique products, or unique words in a text.

💼 Career

Understanding sets is important for data cleaning, removing duplicates, and improving program efficiency in many programming jobs.

1

Create a list with repeated fruits

Create a list called fruits with these exact values: 'apple', 'banana', 'apple', 'orange', 'banana', 'grape'.

Python

# Create the list called fruits with repeated fruit names
# Your code here

Hint

Use square brackets [] to create a list and separate items with commas.

2

Create a set from the list

Create a set called unique_fruits by converting the fruits list into a set using the set() function.

Python

fruits = ['apple', 'banana', 'apple', 'orange', 'banana', 'grape']
# Create a set called unique_fruits from the fruits list
# Your code here

Hint

Use the set() function to remove duplicates from the list.

3

Print the unique fruits

Use print() to display the unique_fruits set so you can see the unique fruit names without duplicates.

Python

fruits = ['apple', 'banana', 'apple', 'orange', 'banana', 'grape']
unique_fruits = set(fruits)
# Print the unique_fruits set
# Your code here

Hint

Use print() to show the contents of the set.

4

Understand the output

Run the program and observe the output. Notice that the printed set shows only unique fruit names without any repeats.

Python

fruits = ['apple', 'banana', 'apple', 'orange', 'banana', 'grape']
unique_fruits = set(fruits)
print(unique_fruits)
# Run the code and see the unique fruits printed

Hint

The order of items in a set can vary, but all items will be unique.

Practice

1. Which of the following is the main reason to use a set in Python?

easy

A. To store unique items without duplicates

B. To keep items in a specific order

C. To allow duplicate values

D. To store key-value pairs

Solution

1. Step 1: Understand the purpose of sets

   Sets automatically remove duplicate items, so they only keep unique elements.

2. Step 2: Compare with other data types

   Lists allow duplicates and keep order, dictionaries store key-value pairs, so they don't fit the main use of sets.

3. Final Answer:

   To store unique items without duplicates -> Option A

4. Quick Check:

   Sets = Unique items [OK]

Hint: Sets always keep unique items, no duplicates allowed [OK]

Common Mistakes:

• Thinking sets keep order
• Confusing sets with lists or dictionaries
• Assuming sets allow duplicates

2. Which of the following is the correct way to create a set in Python?

easy

A. my_set = {1, 2, 3}

B. my_set = [1, 2, 3]

C. my_set = (1, 2, 3)

D. my_set = {'a': 1, 'b': 2}

Solution

1. Step 1: Recall set syntax

   Sets are created using curly braces with comma-separated values, like {1, 2, 3}.

2. Step 2: Identify other data types

   Square brackets create lists, parentheses create tuples, and curly braces with key-value pairs create dictionaries.

3. Final Answer:

   my_set = {1, 2, 3} -> Option A

4. Quick Check:

   Curly braces with values = set [OK]

Hint: Use curly braces with values to create sets [OK]

Common Mistakes:

• Using square brackets instead of curly braces
• Confusing sets with dictionaries
• Using parentheses which create tuples

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

my_list = [1, 2, 2, 3, 4, 4, 4]
my_set = set(my_list)
print(my_set)

medium

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

B. [1, 2, 2, 3, 4, 4, 4]

C. {1, 2, 3, 4}

D. (1, 2, 3, 4)

Solution

1. Step 1: Convert list to set

   Using <code>set()</> on a list removes duplicates, so repeated numbers appear only once.

2. Step 2: Understand set output format

   Printing a set shows unique values inside curly braces without duplicates.

3. Final Answer:

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

4. Quick Check:

   set(list with duplicates) = unique values [OK]

Hint: set() removes duplicates from any list or iterable [OK]

Common Mistakes:

• Expecting list output instead of set
• Thinking duplicates remain in set
• Confusing set with tuple or list syntax

4. Find the error in this code that tries to create a set with duplicate values:

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

medium

A. You must convert the set to a list before printing

B. Sets cannot have duplicate values, so this code will cause an error

C. The syntax for creating a set is wrong

D. The code is correct; duplicates are automatically removed

Solution

1. Step 1: Check set behavior with duplicates

   Sets automatically remove duplicates, so writing duplicates in the set literal is allowed but duplicates are ignored.

2. Step 2: Verify syntax and output

   The syntax is correct and printing the set will show unique values only.

3. Final Answer:

   The code is correct; duplicates are automatically removed -> Option D

4. Quick Check:

   Duplicates ignored in sets = code runs fine [OK]

Hint: Duplicates in set literals are ignored, no error occurs [OK]

Common Mistakes:

• Thinking duplicates cause errors in sets
• Believing set syntax is wrong with duplicates
• Trying to convert set to list unnecessarily

5. You have two lists:

list1 = [1, 2, 3, 4]
list2 = [3, 4, 5, 6]

How can you find the common elements between these lists efficiently using sets?

hard

A. Use list1 + list2 to combine and then remove duplicates

B. Use set(list1) & set(list2) to get the intersection

C. Use a for loop to check each element manually

D. Use set(list1) | set(list2) to get the union

Solution

1. Step 1: Convert lists to sets

   Convert both lists to sets to use set operations like intersection.

2. Step 2: Use intersection operator

   The & operator on sets returns elements common to both sets.

3. Final Answer:

   Use set(list1) & set(list2) to get the intersection -> Option B

4. Quick Check:

   Set intersection = common elements [OK]

Hint: Use & operator on sets to find common items fast [OK]

Common Mistakes:

• Using + operator which concatenates lists
• Using union instead of intersection
• Manually looping instead of using sets