Sets

Set Operations in Python

Sets borrow from mathematics. This lesson introduces union (|), intersection (&), difference (-), symmetric difference (^), and subset checks. These operations let you compare and combine datasets in a single expression.

Sets in Python support mathematical operations. You can combine, compare, and find differences between sets using operators.

The | operator returns a new set with all elements from both sets. Duplicates appear only once.

a = {1, 2, 3}
b = {3, 4, 5}
c = a | b
print(sorted(c))

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Output

What will be the output?

x = {1, 2}
y = {2, 3}
print(len(x | y))

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The & operator returns only elements found in both sets.

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

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Output

What will be the output?

x = {'a', 'b', 'c'}
y = {'b', 'c', 'd'}
print(len(x & y))

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The - operator returns elements in the first set that are not in the second.

all_items = {1, 2, 3, 4, 5}
sold = {2, 4}
remaining = all_items - sold
print(sorted(remaining))

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Output

What will be the output?

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

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The ^ operator returns elements that are in one set or the other, but not both.

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

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Output

What will be the output?

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

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You can also check if one set is contained inside another. A set A is a subset of B if every element in A also exists in B.

Subset and superset checks:

a = {1, 2}
b = {1, 2, 3, 4}
 
a.issubset(b)    # True
b.issuperset(a)  # True

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Every required ingredient is in the pantry. So required is a subset of pantry.

required = {'eggs', 'flour'}
pantry = {'eggs', 'flour', 'milk'}
print(required.issubset(pantry))

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Output

What will be the output?

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

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What will be the output?

a = {1, 2, 3}
b = {2, 3, 4}
c = a & b
print(len(c | a))

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What will be the output?

x = {1, 2, 3}
y = {3, 4, 5}
print(len(x - y) + len(y - x))

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What will be the output?

s = {1, 2, 3, 4, 5}
t = {2, 4}
print(t.issubset(s))

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What will be the output?

a = {1, 2, 3}
b = {1, 2, 3}
print(len(a ^ b))

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