Set vs List in Python

Lists and Sets are there in Python too to store a collection of items, but they have many different behaviors, usages, and properties. So let’s go through those in detail with some explanations and example code.

1. List in Python

A List is an ordered, mutable (changeable), and indexable collection that allows duplicate elements.

Key Characteristics of a List:

1. Ordered: Items are stored in a specific order and can be accessed using indexes.
2. Mutable: You can modify a list (add, remove, or change items).
3. Allows Duplicates: A list can have duplicate values.
4. Indexing & Slicing: You can access elements using an index (e.g., list[0]) and slicing (list[1:4]).

Example Usage of List

# Creating a list
my_list = [10, 20, 30, 40, 50, 20]

# Printing the list
print("Original List:", my_list)

# Accessing elements by index
print("First Element:", my_list[0])
print("Last Element:", my_list[-1])

# Modifying an element
my_list[2] = 99
print("Modified List:", my_list)

# Adding an element
my_list.append(60)
print("List after append:", my_list)

# Removing an element
my_list.remove(20)  # Removes the first occurrence of 20
print("List after removing 20:", my_list)

# Slicing a list
print("Sliced List (index 1 to 3):", my_list[1:4])

# Checking for duplicates
print("Count of 20 in list:", my_list.count(20))

Output:

Original List: [10, 20, 30, 40, 50, 20]
First Element: 10
Last Element: 20
Modified List: [10, 20, 99, 40, 50, 20]
List after append: [10, 20, 99, 40, 50, 20, 60]
List after removing 20: [10, 99, 40, 50, 20, 60]
Sliced List (index 1 to 3): [99, 40, 50]
Count of 20 in list: 1

2. Set in Python

A Set is an unordered, mutable collection of unique elements that doesn’t allow any form of duplication.

Key Characteristics of a List:

• Unordered: Elements are not maintained in any sequence.
• Mutable: Elements can be added and deleted but changed isn’t allowed to change any individual element
• Unique Elements: Duplicates will be eliminated from the set.
• No Indexing: It doesn’t have index and its elements can’t be accessed with any index.

Example Usage of Set

# Creating a set
my_set = {10, 20, 30, 40, 50, 20}

# Printing the set
print("Original Set:", my_set)

# Adding an element
my_set.add(60)
print("Set after adding 60:", my_set)

# Removing an element
my_set.remove(30)
print("Set after removing 30:", my_set)

# Checking if an element exists
print("Is 40 in set?", 40 in my_set)

# Performing set operations
set1 = {1, 2, 3, 4, 5}
set2 = {4, 5, 6, 7, 8}

# Union (all unique elements from both sets)
print("Union of set1 and set2:", set1 | set2)

# Intersection (common elements)
print("Intersection of set1 and set2:", set1 & set2)

# Difference (elements in set1 but not in set2)
print("Difference of set1 - set2:", set1 - set2)

# Symmetric Difference (elements in either set, but not both)
print("Symmetric Difference:", set1 ^ set2)

Output:

Original Set: {40, 10, 50, 20, 30}  # Order may vary
Set after adding 60: {40, 10, 50, 20, 60, 30}
Set after removing 30: {40, 10, 50, 20, 60}
Is 40 in set? True
Union of set1 and set2: {1, 2, 3, 4, 5, 6, 7, 8}
Intersection of set1 and set2: {4, 5}
Difference of set1 - set2: {1, 2, 3}
Symmetric Difference: {1, 2, 3, 6, 7, 8}

3. Difference Between List and Set

4. When to Use List vs Set?

Use a List when:

• You need to keep the order of elements.
• You need to store duplicate values.
• You need to access elements by their index.

Use a Set when:

• You need only unique values.
• You want fast lookups (checking if an item exists is faster in a set).
• Order of elements doesn’t matter.

Final Thoughts

• Use a List if you need an ordered collection that permits duplicates.
• If you need a collection of unique elements and don’t care about the order, use a Set.