Sets in Python Explained with Examples

Introduction to Sets in Python

A set in Python is a built-in data structure used to store unique values. Sets are particularly useful when working with collections where duplicates are not allowed or when performing mathematical set operations such as union and intersection.

Python sets are optimized for performance and are commonly used in real-world applications involving data validation, filtering, and comparison.

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Key Characteristics of Python Sets

• Stores only unique elements
• Unordered collection (no indexing)
• Mutable (elements can be added or removed)
• Supports multiple data types
• Uses hashing for fast lookups

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Creating Sets in Python

collection1 = {1, 2, 3, 4}

Important note:
An empty set must be created using set().
Using {} creates an empty dictionary, not a set.

collection4 = set()

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How Sets Handle Duplicate Values

Input Values:   1, 2, 3, 4, 4, 3, 2, 1
Set Output:    {1, 2, 3, 4}

Duplicate values are automatically removed when a set is created.

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Example Code: Understanding Sets Step by Step

collection1 = {1, 2, 3, 4}

collection2 = {1, 2, 3, 4, "Hi", "Hello", "Bye", 1.0}

collection3 = {1, 2, 3, 4, 4, 3, 2, 1}

collection4 = set()

Explanation

• collection1 contains only integers
• collection2 contains mixed data types
• collection3 demonstrates automatic removal of duplicates
• collection4 is an empty set

Note:
1 and 1.0 are considered the same value in a set.

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Checking Type and Length of a Set

print(type(collection1))
print(len(collection1))

The len() function counts only unique elements.

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Adding Elements to a Set

collection4.add(1)
collection4.add(2)
collection4.add(3)
collection4.add(4)
collection4.add(1)   # Duplicate value ignored

Sets do not allow duplicate entries, so adding the same value again has no effect.

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Removing Elements from a Set

remove() Method

collection4.remove(3)

• Removes a specific element
• Raises a KeyError if the element does not exist

# collection4.remove(5)  # Raises KeyError

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Difference Between remove() and pop() in Sets

Feature	remove()	pop()
Removes	Specific element	Random element
Argument required	Yes	No
Predictable removal	Yes	No
Error if element missing	Yes	Yes

pop() Example

removed_item = collection4.pop()

Because sets are unordered, the element removed by pop() is unpredictable.

Before pop(): {1, 2, 3, 4}
After pop():  {1, 3, 4}  (example output)

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Clearing All Elements from a Set

collection4.clear()

The clear() method removes all elements and leaves the set empty.

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Set Operations in Python

Union

collection1.union(collection2)

Returns all unique elements from both sets.

Intersection

collection1.intersection(collection2)

Returns only the common elements.

Set A: {1, 2, 3, 4}
Set B: {3, 4, 5, 6}

Union:        {1, 2, 3, 4, 5, 6}
Intersection: {3, 4}

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What Can and Cannot Be Stored in a Set

collection4.add((6, 7, 8))   # Allowed (tuple)
collection4.add([9, 10])    # Not allowed (list)

Only immutable (hashable) data types can be stored in a set.

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Real-World Use Cases of Python Sets

• Removing duplicate values from data
• Tracking unique user sessions
• Comparing datasets
• Filtering unique records
• Validating input data

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