More on Sets

Let’s explore sets in Python with easy explanations, emojis, practical examples, and practice questions! 🎯🧑‍💻

What is a Set? 🥇

A set in Python is an unordered collection of unique and immutable elements.

• Unordered: No item has a fixed position (no indexing or slicing).
• Unique: Each element appears only once.
• Mutable: You can add or remove items, but the items themselves must be immutable (like numbers, strings, or tuples).

How to Create a Set 🛠️

• Using curly braces {}:

my_set = {1, 2, 3, 4}
print(my_set)  # Output: {1, 2, 3, 4}

• Using the set() function (especially for empty sets):

empty_set = set()
print(empty_set)  # Output: set()

Note: {} creates an empty dictionary, not a set!

Key Features of Sets ⭐

• No duplicates:

s = {1, 2, 2, 3}
print(s)  # Output: {1, 2, 3}

• No indexing: You cannot do s or s[^1]—sets are unordered!
• Can add and remove items: But only immutable types can be members (no lists or dicts).

Set Methods & Operations 🧰

Set Operations in Action 🚦

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

print(a | b)  # Union: {1, 2, 3, 4, 5}
print(a & b)  # Intersection: {3}
print(a - b)  # Difference: {1, 2}
print(a ^ b)  # Symmetric Difference: {1, 2, 4, 5}

Set Comprehensions 🧑‍🎨

Just like list comprehensions, but with {}:

squares = {x*x for x in range(5)}
print(squares)  # Output: {0, 1, 4, 9, 16}

Limitations 🚫

• No indexing/slicing: You cannot access elements by position.
• Only immutable items: You can’t put lists or dictionaries in a set, but you can use tuples.
• Unordered: The order of elements is not preserved.

Practice Questions & Solutions 📝

1️⃣ Create a set with the numbers 1, 2, 2, 3, 4. How many elements will it have?

s = {1, 2, 2, 3, 4}
print(len(s))  # Output: 4

2️⃣ Add the number 5 to the set {1, 2, 3}.

s = {1, 2, 3}
s.add(5)
print(s)  # Output: {1, 2, 3, 5}

3️⃣ Remove 2 from the set {1, 2, 3} using both remove() and discard(). What happens if you try to remove 10?

s = {1, 2, 3}
s.remove(2)     # Works fine
# s.remove(10)  # Raises KeyError

s = {1, 2, 3}
s.discard(10)   # No error, does nothing

4️⃣ Find the intersection and union of {1, 2, 3} and {2, 3, 4}.

a = {1, 2, 3}
b = {2, 3, 4}
print(a & b)  # Intersection: {2, 3}
print(a | b)  # Union: {1, 2, 3, 4}

5️⃣ Use set comprehension to create a set of even numbers from 0 to 10.

evens = {x for x in range(11) if x % 2 == 0}
print(evens)  # Output: {0, 2, 4, 6, 8, 10}

When to Use Sets? 🤔

• When you need to store unique items.
• When you want to do fast membership tests (x in s is very fast).
• When you need to perform mathematical set operations (union, intersection, etc.).

Key Points with Emojis 🎯

• Sets are unordered collections of unique items: {a, b, c}
• No duplicates allowed
• No indexing or slicing
• Great for membership tests and set operations (union, intersection, difference)
• Mutable: You can add or remove items

If you want to know about frozen sets (immutable sets) or have more questions, just ask! 😃

References: Sets are unordered, unique collections in Python, created with curly braces or the set() function, supporting mathematical set operations and various methods for adding, removing, and testing membership¹².