← Python

Lists + Dictionaries

A list of dictionaries represents a table of records where each dict is one row

What it does: & gives items that appear in both sets. 2 and 3 are in both a and b. - is difference — items in the left set but not the right. ^ is symmetric difference — items in either set but not both. Think of | as 'OR' — items in set A OR set B (or both). Think of & as 'AND' — items in set A AND set B. issubset checks if every item in the first set exists in the second. union() and | both combine all items — intersection() and & find common items. | & - ^ all return new sets; use |= &= etc. to modify in place.

Common mistakes: Sets don't support + for union. Use | or .union(). Use & for set intersection, not 'and' (which is a boolean operator).

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Learning

Duo

{1,2,3} | {3,4,5} returns?

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

Matches

❌ a = {1,2} b = [3,4] a | b

↓

Error: Both must be sets for |

Applying

Meanings

Term

Union

Meaning

Combines all items from both sets with no duplicates.

Practice

a = {1, 2, 3}

Testing

Gaps

print(a b)

Check Answer

Spots

2b = {3, 4}

3print(a + b)

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Quick Questions

1. {1,2,3} | {3,4,5} returns?

A. {1, 2, 3, 4, 5} ✓

B. {3}

| is union — all items from both sets, duplicates removed

2. {1,2,3} & {2,3,4} returns?

A. {1, 2, 3, 4}

B. {2, 3} ✓

& is intersection — only items that appear in both sets

3. {1,2,3} - {2,3,4} returns?

A. {1} ✓

B. {4}

- is difference — items in the left set but not the right

4. {1,2,3} ^ {2,3,4} returns?

A. {2, 3}

B. {1, 4} ✓

^ is symmetric difference — items in either set but not both

5. What does | do with sets?

A. Union combines all items ✓

B. Intersection

Think of | as 'OR' — items in set A OR set B (or both)

Match the Pairs

a = {1,2} b = [3,4] a | b → Error: Both must be sets for |

s = {1,2,3} s.add([4,5]) → Error: Lists can't be set elements

a = {1,2,3} b = {2,3,4} a & b → Valid: Intersection {2, 3}

a = {1,2,3} b = {2,3,4} a - b → Ok: Difference {1}

a={1,2} b={2,3} print(a | b) → Output: {1, 2, 3}

a={1,2} b={2,3} print(a & b) → Output: {2}

Key Term

Union

Combines all items from both sets with no duplicates.~~Intersection

Fill in the Blanks

1. a = {1, 2, 3} b = {3, 4} print(a | b)

2. a = {1, 2, 3} b = {2, 3, 4} print(a & b)

3. a = {1, 2, 3} b = {2, 3} print(a - b)

4. a = {1, 2} b = {1, 2, 3} print(a.issubset(b))

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

Spot the Error

Question 1

A a = {1, 2, 3}

B b = {3, 4}

C print(a + b)

Line C — Sets don't support + for union. Use | or .union().

Question 2

A a = {1, 2, 3}

B b = {2, 3, 4}

C print(a and b)

Line C — Use & for set intersection, not 'and' (which is a boolean operator)

Question 3

A a = {1, 2, 3}

B b = {2, 3, 4}

C print(a or b)

Line C — Use | for set union, not 'or' (which is a boolean operator)

Question 4

A a = {1, 2, 3}

B b = {3, 4}

C combined = a.union[b]

D print('Union:', combined)

Line C — Use parentheses () to call methods, not square brackets []

Question 5

A print({1, 2}.subset({1, 2, 3}))

B a = {1, 2}

C b = {1, 2, 3}

D print('Done')

Line A — The method is issubset(), not subset()

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