Set in Python

A set in Python is a built-in data type used to store multiple unique values in a single variable.

It is mainly used when:

• You want to avoid duplicate values
• You need fast searching
• You want to perform mathematical set operations like union and intersection

What is a Set?

A set is a collection of unique elements.

• Unordered: Items are not stored in a particular order.
• Mutable: You can add or remove elements.
• No duplicate elements: Each item appears only once.

Example:

my_set = {1, 2, 3, 4, 5}
print(my_set)  
# Output: {1, 2, 3, 4, 5}

Creating a Set

s = set()

# set with element
s = {1,2,3,4}

# Duplicate values are automatically removed
s = {1,2,2,3,4}
print(s)
# {1,2,3,4}

Note:

• {} creates an empty dictionary
• Use set() for an empty set

Characteristics of Set

• Unordered
• No indexing
• No duplicates
• Mutable (can be changed)
• Elements must be immutable (no list inside set)

Accessing Elements

Since sets are unordered, you cannot use index.

s = {10, 20, 30}

for item in s:
    print(item)

Adding Elements

1. add() (Add One Element)

s = {1,2,3}
s.add(4)
print(s)
# output
  # {1, 2, 3, 4}

2. update() (Add Multiple Elements)

s.update([5, 6, 7])
print(s)
# ouput
  # {1, 2, 3, 5, 6, 7}

Removing Elements

1. remove()

Removes an element.
Raises error if element does not exist.

s.remove(2)
print(s)
# output
  # {1, 3}

2. discard()

Removes an element.
Does NOT raise error if element not found.

s.discard(10)

3. pop()

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Removes a random element.

s.pop()

4. clear()

Removes all elements.

s.clear()

Set Operations

Sets support mathematical operations.

1. Union (|)

• Combines both sets.

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

print(A | B)
# ouput
  # {1, 2, 3, 4, 5}

2. Intersection (&)

• Common elements only.

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

print(A & B)
# ouput
  # {3}

3. Difference (-)

• Elements in first set but not in second.

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

print(A - B)
# ouput
  # {1, 2}

4. Symmetric Difference (^)

• Elements not common in both sets.

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

print(A ^ B)
# ouput
  # {1, 2, 4, 5}

Frozen Set

• If you want an immutable set, use frozenset().

fs = frozenset([1, 2, 3])
print(fs)

Frozen sets:

• Cannot be modified
• Can be used as dictionary keys

When Should You Use a Set?

Use a set when:

• You need unique values
• You want fast lookup
• You need mathematical operations
• Order does not matter

Questions

1. What is a set in Python?
2. Why are sets unordered?
3. Can sets contain duplicate values?
4. What is the difference between remove() and discard()?
5. What is the internal working of a set?
6. What is a frozenset?
7. Explain union, intersection, difference.

Table of Contents

• Python: A Beginner’s Guide to Programming