Union and intersection in Python - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a union of two sets.

Python

set1 = {1, 2, 3}
set2 = {3, 4, 5}
result = set1 [1] set2
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 | results in intersection, not union.

Using + causes an error because sets don't support +.

The | operator creates a union of two sets, combining all unique elements.

2fill in blank

medium

Complete the code to find the intersection of two sets.

Python

a = {10, 20, 30}
b = {20, 40, 50}
common = a [1] b
print(common)

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

A&

B|

C-

D^

Attempts:

3 left

💡 Hint

Common Mistakes

Using | results in union, not intersection.

Using - gives difference, not intersection.

The & operator finds the intersection of two sets, elements common to both.

3fill in blank

hard

Fix the error in the code to get the union of two sets.

Python

set_a = {1, 2}
set_b = {2, 3}
union_set = set_a.[1](set_b)
print(union_set)

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

Aunion

Bintersect

Cadd

Dappend

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'intersect' which is not a valid set method.

Using 'add' or 'append' which are for adding single elements.

The correct method to get the union of two sets is union().

4fill in blank

hard

Fill both blanks to create a dictionary with word lengths for words longer than 3 letters.

Python

words = ['apple', 'bat', 'carrot', 'dog']
lengths = {word: [1] for word in words if len(word) [2] 3}
print(lengths)

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

Alen(word)

Bword

C>

D<=

Attempts:

3 left

💡 Hint

Common Mistakes

Using word instead of length for values.

Using <= instead of > in the condition.

The dictionary comprehension uses len(word) for values and filters words with length greater than 3 using >.

5fill in blank

hard

Fill all three blanks to create a dictionary of uppercase words with their lengths for words longer than 3 letters.

Python

words = ['apple', 'bat', 'carrot', 'dog']
result = [1]: [2] for w in words if len(w) [3] 3}
print(result)

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

Aw.upper()

Blen(w)

C>

Dw.lower()

Attempts:

3 left

💡 Hint

Common Mistakes

Using w.lower() instead of uppercase.

Using <= instead of > in the condition.

The dictionary comprehension uses w.upper() as keys, len(w) as values, and filters words longer than 3 with >.

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