Union and intersection in Python - Mini Project: Build & Apply

Union and Intersection of Sets

📖 Scenario: You are organizing a community event and have two lists of people who signed up for two different activities. You want to find out who signed up for either activity and who signed up for both.

🎯 Goal: Build a Python program that finds the union and intersection of two sets of names.

📋 What You'll Learn

Create two sets with exact names

Create a variable for union of the two sets

Create a variable for intersection of the two sets

Print the union and intersection sets

💡 Why This Matters

🌍 Real World

Finding union and intersection is useful when combining or comparing groups of people, items, or data in real life, like event planning or inventory management.

💼 Career

Understanding set operations is important in data analysis, software development, and database management where you often need to combine or filter data.

1

Create two sets of names

Create a set called activity1 with these exact names: 'Alice', 'Bob', 'Charlie'. Also create a set called activity2 with these exact names: 'Bob', 'Diana', 'Edward'.

Python

# Create the sets activity1 and activity2 with the exact names
# Your code here

Hint

Use curly braces {} to create sets and separate names with commas.

2

Create union and intersection variables

Create a variable called union_set that stores the union of activity1 and activity2. Create another variable called intersection_set that stores the intersection of activity1 and activity2.

Python

activity1 = {'Alice', 'Bob', 'Charlie'}
activity2 = {'Bob', 'Diana', 'Edward'}
# Create union_set and intersection_set variables
# Your code here

Hint

Use the .union() method for union and .intersection() method for intersection.

3

Print the union and intersection sets

Write two print statements: one to display union_set and one to display intersection_set.

Python

activity1 = {'Alice', 'Bob', 'Charlie'}
activity2 = {'Bob', 'Diana', 'Edward'}
union_set = activity1.union(activity2)
intersection_set = activity1.intersection(activity2)
# Print union_set and intersection_set
# Your code here

Hint

Use print() to show the sets on the screen.

4

Run and check the output

Run the program and check that the output shows the union set with all unique names and the intersection set with names common to both activities.

Python

activity1 = {'Alice', 'Bob', 'Charlie'}
activity2 = {'Bob', 'Diana', 'Edward'}
union_set = activity1.union(activity2)
intersection_set = activity1.intersection(activity2)
print(union_set)
print(intersection_set)
# Run the program to see the output

Hint

The first printed set should have all five unique names. The second printed set should have only 'Bob'.

Practice

1. What does the union operation do when applied to two sets in Python?

easy

A. Combines all unique elements from both sets

B. Finds elements only in the first set

C. Finds elements only in the second set

D. Finds elements common to both sets

Solution

1. Step 1: Understand union operation

   The union of two sets includes every unique element from both sets without duplicates.

2. Step 2: Compare with other options

   Options B and C describe subsets, and D describes intersection, not union.

3. Final Answer:

   Combines all unique elements from both sets -> Option A

4. Quick Check:

   Union = all unique elements combined [OK]

Hint: Union joins all unique items from both sets [OK]

Common Mistakes:

• Confusing union with intersection
• Thinking union only takes elements from one set
• Assuming union keeps duplicates

2. Which of the following is the correct syntax to find the intersection of two sets a and b in Python?

easy

A. a + b

B. a | b

C. a & b

D. a - b

Solution

1. Step 1: Recall intersection syntax

   In Python, the intersection of two sets is found using the & operator or the .intersection() method.

2. Step 2: Check other operators

   | is union, + is invalid for sets, - is difference.

3. Final Answer:

   a & b -> Option C

4. Quick Check:

   Intersection uses & operator [OK]

Hint: Use & for intersection of sets [OK]

Common Mistakes:

• Using | instead of & for intersection
• Trying to add sets with + operator
• Confusing difference (-) with intersection

3. What is the output of the following code?

set1 = {1, 2, 3, 4}
set2 = {3, 4, 5, 6}
print(set1.intersection(set2))

medium

A. {1, 2}

B. {5, 6}

C. {1, 2, 3, 4, 5, 6}

D. {3, 4}

Solution

1. Step 1: Identify intersection elements

   The intersection contains elements present in both sets: {3, 4}.

2. Step 2: Confirm output

   Printing the intersection returns {3, 4} exactly.

3. Final Answer:

   {3, 4} -> Option D

4. Quick Check:

   Common elements = {3, 4} [OK]

Hint: Intersection shows only common elements [OK]

Common Mistakes:

• Confusing union with intersection output
• Expecting all elements combined
• Mixing up set contents

4. The following code is intended to print the union of two sets, but it causes an error. What is the problem?

set1 = {1, 2, 3}
set2 = {3, 4, 5}
print(set1 + set2)

medium

A. Sets cannot be added with + operator

B. The sets are empty

C. The print statement is missing parentheses

D. The sets have overlapping elements

Solution

1. Step 1: Identify the error cause

   Python sets do not support the + operator; this causes a TypeError.

2. Step 2: Correct way to union sets

   Use | operator or .union() method to combine sets.

3. Final Answer:

   Sets cannot be added with + operator -> Option A

4. Quick Check:

   + operator invalid for sets [OK]

Hint: Use | or .union(), not + for sets [OK]

Common Mistakes:

• Trying to add sets with +
• Ignoring error message
• Confusing list addition with set union

5. Given two lists of student names, list1 = ['Anna', 'Bob', 'Cara'] and list2 = ['Bob', 'Diana', 'Anna'], which Python code correctly finds students present in both lists using set operations?

hard

A. list1 | list2

B. set(list1) & set(list2)

C. set(list1) + set(list2)

D. list1.intersection(list2)

Solution

1. Step 1: Convert lists to sets for set operations

   Lists must be converted to sets to use intersection (&) operator.

2. Step 2: Use & operator to find common elements

   set(list1) & set(list2) returns elements in both sets.

3. Step 3: Check other options

   list1 | list2 uses | on lists (invalid), C uses + on sets (invalid), D calls intersection on list (no such method).

4. Final Answer:

   set(list1) & set(list2) -> Option B

5. Quick Check:

   Convert lists to sets, then & for intersection [OK]

Hint: Convert lists to sets before intersection [OK]

Common Mistakes:

• Using + or | on lists directly
• Calling set methods on lists
• Not converting lists to sets first