Difference and symmetric difference in Python - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the difference() method do in Python sets?

It returns a new set with elements that are in the first set but not in the second set.

beginner

What is the result of {1, 2, 3}.difference({2, 3, 4})?

The result is {1} because 1 is only in the first set, not in the second.

beginner

What does the symmetric_difference() method do in Python sets?

It returns a new set with elements that are in either of the sets but not in both.

beginner

What is the result of {1, 2, 3}.symmetric_difference({2, 3, 4})?

The result is {1, 4} because 1 and 4 are in only one of the sets, not both.

intermediate

How is symmetric difference different from difference?

Difference gives elements only in the first set. Symmetric difference gives elements in either set but not in both.

What does {1, 2, 3} - {2, 4} return?

A {4}

B {1, 3}

C {2}

D {1, 2, 3, 4}

The difference removes elements in the second set from the first, so {1, 3} remains.

Which method returns elements in either set but not both?

A difference()

B intersection()

C union()

D symmetric_difference()

symmetric_difference() returns elements exclusive to each set, excluding common elements.

What is the output of {5, 6}.symmetric_difference({6, 7})?

A {5, 6, 7}

B {6}

C {5, 7}

D {}

Elements 5 and 7 are in only one set each, so they form the symmetric difference.

If A = {1, 2, 3} and B = {2, 3, 4}, what is A.difference(B)?

A {1}

B {1, 4}

C {2, 3}

D {4}

Only 1 is in A but not in B, so difference returns {1}.

Which operator is equivalent to symmetric_difference()?

A ^

B &

C -

D |

The caret (^) operator returns the symmetric difference of two sets.

Explain in your own words the difference between the difference and symmetric difference of two sets.

Think about what elements are left after removing common ones.

Write a Python code snippet that shows how to find the symmetric difference between two sets and print the result.

Use sets like {1, 2} and {2, 3} to see what changes.

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