🧩 Learn how to work with sets in Python — an unordered collection of unique, immutable elements.

Sets are powerful for tasks like removing duplicates, performing mathematical set operations (union, intersection, difference), and checking membership efficiently.

A set is an unordered collection of unique items. It supports:

• Membership testing (in)
• Iteration
• Mathematical operations like union, intersection, and difference

• Elements must be immutable (e.g., numbers, strings, tuples)
• Elements are not duplicated
• Order of elements is not guaranteed

skills = {'Python programming', 'Databases', 'Software design'}

🔸 You can also create a set from an iterable:

chars = set('letter')  # {'l', 'e', 't', 'r'}

⚠️ Don’t use {} – it creates an empty dictionary, not a set.

empty_set = set()

Since sets are unordered, you cannot access elements by index.

🔹 Use a for loop or in operator:

for skill in skills:
    print(skill)

print('Python programming' in skills)  # True

Use .add() to insert a new element.

skills.add('Problem solving')

🔸 If the element already exists, no error is raised and nothing changes.

There are several methods to remove elements based on your needs:

skills.remove('Databases')     # May raise KeyError
skills.discard('Java')         # Safe removal
skills.pop()                   # Remove random item
skills.clear()                 # Empty the set

Returns a new set containing all elements from both sets.

set1 = {'Python', 'Java'}
set2 = {'C++', 'JavaScript'}
combined = set1 | set2
# OR
combined = set1.union(set2)

🔸 .union() accepts any iterable, while | only works with sets.

Returns elements common to all sets.

s1 = {'Python', 'Java'}
s2 = {'Java', 'C++'}
common = s1 & s2  # {'Java'}

Returns elements in the first set that are not in the second.

s1 = {'Python', 'Java'}
s2 = {'Java', 'C++'}
diff = s1 - s2  # {'Python'}

Returns elements present in either set but not both.

s1 = {'Python', 'Java'}
s2 = {'Java', 'C++'}
result = s1 ^ s2  # {'Python', 'C++'}

Check if all elements of one set are in another.

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

print(a.issubset(b))  # True
print(a <= b)          # True
print(a < b)           # True (proper subset)

Check if a set contains all elements of another.

print(b.issuperset(a))  # True
print(b >= a)            # True
print(b > a)             # True (proper superset)

Two sets are disjoint if they have no elements in common.

set1 = {1, 2}
set2 = {3, 4}
print(set1.isdisjoint(set2))  # True

Create sets using concise syntax.

{expression for element in iterable if condition}

tags = {'Django', 'Pandas', 'Numpy'}
lower_tags = {tag.lower() for tag in tags}

numbers = {1, 2, 3, 4, 5}
evens = {n for n in numbers if n % 2 == 0}

To make a set immutable, wrap it in frozenset().

skills = frozenset({'Python', 'SQL'})

🔸 Attempting to modify will raise an error:

skills.add('Git')  # ❌ AttributeError

skills = {'Problem solving', 'Design', 'Python'}
print(len(skills))  # Output: 3
print('Design' in skills)  # True

• Order is not preserved – don’t rely on element position.
• Duplicates are removed automatically when creating or updating a set.
• Use set() with lists/tuples to easily remove duplicates.
• frozenset is useful for keys in dictionaries or as elements in other sets.
• Use set.intersection() over & if working with non-set iterables.

🎉 Congratulations! You now have a solid understanding of Python Sets — including how to define them, perform set operations, and use them effectively in real-world scenarios.

Next up: ⚠️ Section 8: Exception Handling – learn how to handle errors gracefully in your programs!