Difference and symmetric difference in Python - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of set difference operation

What is the output of this Python code?

Python

a = {1, 2, 3, 4}
b = {3, 4, 5, 6}
result = a - b
print(result)

A {1, 2, 3, 4, 5, 6}

B {3, 4}

C {5, 6}

D {1, 2}

💡 Hint

Remember, set difference returns elements in the first set not in the second.

The difference a - b returns elements in a that are not in b, which are 1 and 2.

❓ Predict Output

intermediate

Output of symmetric difference operation

What does this code print?

Python

x = {10, 20, 30}
y = {20, 40, 50}
print(x ^ y)

A {10, 30, 40, 50}

B {10, 20, 30, 40, 50}

C {20}

D {40, 50}

💡 Hint

Symmetric difference returns elements in either set but not both.

The symmetric difference excludes 20 because it is in both sets, leaving 10, 30, 40, and 50.

🧠 Conceptual

advanced

Understanding difference with empty set

What is the result of the difference operation when subtracting an empty set from a non-empty set?

A The original non-empty set

B An empty set

C A set with all elements doubled

D A set with elements removed randomly

💡 Hint

Think about what elements are removed when subtracting nothing.

Subtracting an empty set removes no elements, so the original set remains unchanged.

❓ Predict Output

advanced

Result of chained symmetric difference

What is the output of this code?

Python

a = {1, 2, 3}
b = {2, 3, 4}
c = {3, 4, 5}
result = a ^ b ^ c
print(result)

A {1, 4, 5}

B {1, 2, 5}

C {1, 3, 5}

D {2, 3, 4, 5}

💡 Hint

Symmetric difference is associative; think step-by-step.

First a ^ b = {1, 4}, then {1, 4} ^ c = {1, 3, 5}.

🔧 Debug

expert

Identify the error in set difference code

Which option will cause an error when run?

Python

s1 = {1, 2, 3}
s2 = [2, 3, 4]
result = s1 - s2
print(result)

A s1.difference(s2)

B s1 - s2

C s1 - set(s2)

D s1.symmetric_difference(s2)

💡 Hint

Check the types used in the difference operation.

Subtracting a list from a set with '-' operator raises a TypeError.

Practice

1. What does the difference operation A - B return when applied to two sets A and B?

easy

A. All elements from both A and B

B. Elements in B but not in A

C. Elements in A but not in B

D. Elements common to both A and B

Solution

1. Step 1: Understand the difference operation

   The difference A - B means all elements that are in A but not in B.

2. Step 2: Compare options with definition

   Elements in A but not in B matches this definition exactly, others describe different set operations.

3. Final Answer:

   Elements in A but not in B -> Option C

4. Quick Check:

   Difference = Elements only in first set [OK]

Hint: Difference = items only in the first set [OK]

Common Mistakes:

• Confusing difference with symmetric difference
• Thinking difference includes elements from both sets
• Mixing up order of sets in difference

2. Which of the following is the correct syntax to find the symmetric difference between 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 symmetric difference operator

   In Python, symmetric difference between sets is found using the ^ operator.

2. Step 2: Match operators to meanings

   - is difference, | is union, & is intersection, so only ^ is correct for symmetric difference.

3. Final Answer:

   A ^ B -> Option A

4. Quick Check:

   Symmetric difference uses ^ operator [OK]

Hint: Use ^ for symmetric difference in Python [OK]

Common Mistakes:

• Using - instead of ^ for symmetric difference
• Confusing union (|) with symmetric difference
• Using & which is intersection, not symmetric difference

3. What is the output of the following code?

 A = {1, 2, 3, 4} 
 B = {3, 4, 5, 6} 
 print(A - B) 

medium

A. {3, 4}

B. {1, 2}

C. {5, 6}

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

Solution

1. Step 1: Calculate difference A - B

   Elements in A are {1, 2, 3, 4}, in B are {3, 4, 5, 6}. Difference A - B is elements in A not in B, which are {1, 2}.

2. Step 2: Verify output matches options

   {1, 2} is {1, 2}, which matches the calculated difference.

3. Final Answer:

   {1, 2} -> Option B

4. Quick Check:

   A - B = {1, 2} [OK]

Hint: Difference removes items found in second set [OK]

Common Mistakes:

• Including elements common to both sets
• Confusing difference with union
• Swapping sets order in difference

4. The following code is intended to print the symmetric difference of sets A and B. What is the error?

 A = {1, 2, 3} 
 B = {2, 3, 4} 
 print(A -^ B) 

medium

A. Prints the union of A and B

B. Prints the difference of A and B

C. Prints the intersection of A and B

D. SyntaxError due to invalid operator '-^'

Solution

1. Step 1: Identify the operator used

   The code uses -^ which is not a valid Python operator.

2. Step 2: Understand correct symmetric difference syntax

   Symmetric difference uses ^ alone, not combined with -. So this causes a syntax error.

3. Final Answer:

   SyntaxError due to invalid operator '-^' -> Option D

4. Quick Check:

   Invalid operator causes SyntaxError [OK]

Hint: Use ^ alone for symmetric difference, no combined operators [OK]

Common Mistakes:

• Combining - and ^ operators incorrectly
• Trying to use -^ as a single operator
• Not recognizing syntax errors from invalid operators

5. Given two sets A = {1, 2, 3, 4, 5} and B = {4, 5, 6, 7}, which expression returns a set of elements that are in either A or B but not in both, and also excludes the element 7 if present?

hard

A. (A ^ B) - {7}

B. (A - B) | (B - A) | {7}

C. (A | B) - {7}

D. (A & B) - {7}

Solution

1. Step 1: Understand symmetric difference and exclusion

   Symmetric difference A ^ B gives elements in either set but not both. To exclude 7, subtract {7}.

2. Step 2: Analyze options

   (A ^ B) - {7} correctly computes symmetric difference then removes 7. (A - B) | (B - A) | {7} incorrectly adds {7}. (A | B) - {7} is union minus 7, which includes common elements. (A & B) - {7} is intersection minus 7, which is wrong.

3. Final Answer:

   (A ^ B) - {7} -> Option A

4. Quick Check:

   Symmetric difference minus {7} = (A ^ B) - {7} [OK]

Hint: Subtract {7} after symmetric difference to exclude it [OK]

Common Mistakes:

• Using union instead of symmetric difference
• Adding {7} instead of subtracting
• Using intersection which is common elements only