8.2.6. Set Operations

Sets support mathematical operations that make it easy to compare two collections. Each operation has both an operator shorthand and a method form which produce the same result:

Operation	Operator	Method	Description
Union	a | b	a.union(b)	All elements from both sets
Intersection	a & b	a.intersection(b)	Only elements common to both sets
Difference	a - b	a.difference(b)	Elements in a but not in b
Symmetric Difference	a ^ b	a.symmetric_difference(b)	Elements in either set, but not in both

import sys
from pathlib import Path

# Find project root by looking for _config.yml
current = Path.cwd()
for parent in [current, *current.parents]:
    if (parent / '_config.yml').exists():
        project_root = parent
        break
else:
    project_root = Path.cwd().parent.parent

# Add project root to path
sys.path.insert(0, str(project_root))

# Import shared teaching helpers and cell magics
from shared import thinkpython, diagram, jupyturtle, structshape
from shared.download import download

a = {1, 2, 3}
b = {3, 4, 5}

Note that, operator forms (|, &, -, ^) require set operands. Method forms are more flexible and can take any iterable.

print(a.union([3, 4, 5]))    # works: method accepts iterable

try:
    a | [3, 4, 5]            # TypeError: right side is a list
except TypeError as e:
    print(e)

{1, 2, 3, 4, 5}
unsupported operand type(s) for |: 'set' and 'list'

8.2.6.1. Union

All elements from both sets

a | b        # {1, 2, 3, 4, 5}
a.union(b)   # same

{1, 2, 3, 4, 5}

8.2.6.2. Intersection

Only elements in both sets.

a & b              # {3}
a.intersection(b)  # same

{3}

8.2.6.3. Difference

Elements in a but not in b

a - b              # {1, 2}
a.difference(b)    # same

{1, 2}

8.2.6.4. Symmetric Difference

Elements in either set, but not both

a ^ b                       # {1, 2, 4, 5}
a.symmetric_difference(b)   # same

{1, 2, 4, 5}

### Exercise: Basic Set Operations
# 1. Create A = {1, 2, 3, 4} and B = {3, 4, 5, 6}.
# 2. Print A | B, A & B, A - B, and A ^ B.
### Your code starts here.




### Your code ends here.

Show code cell source

Hide code cell source

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

print("Union:", A | B)
print("Intersection:", A & B)
print("Difference A-B:", A - B)
print("Symmetric Difference:", A ^ B)

Union: {1, 2, 3, 4, 5, 6}
Intersection: {3, 4}
Difference A-B: {1, 2}
Symmetric Difference: {1, 2, 5, 6}