02 CDT - 06 Sets

A set is an unordered collection of unique elements. Unlike sequences (such as lists or tuples), sets are unordered and do not store duplicate elements. Since sets are unordered, they do not support indexing, slicing, or other sequence-like behavior.

Sets are commonly used for operations like checking membership, removing duplicates, and performing mathematical set operations.

Key Characteristics of Sets:

• Mutable: You can add or remove elements from a set after it is created.
• Unordered: The elements in a set do not have a specific order, and you cannot access elements by index.
• No duplicates: Sets automatically remove any duplicate elements, ensuring that all elements are unique.

Creating a set looks similar to dictionary but is not having key value pairs.

s = {1, 2, 3, 4}

Adding and Removing Elements

• update(): Adds multiple elements to the set (from an iterable).
• remove(): Removes a specific element from the set. Raises a KeyError if the element doesn’t exist.
• discard(): Removes a specific element from the set, but does not raise an error if the element doesn’t exist.

‘set.update()’

The update() method is used to add multiple elements to a set. You can pass any iterable (e.g., a list, tuple, or another set) to the update() method, and it will add all the elements from the iterable to the set.

Note: update() does not add duplicates to the set, as sets do not allow duplicate elements.

>>> s = {1,2,3}
>>> type(s)
<class 'set'>

>>> s.update([4])
>>> s   # passing list
{1, 2, 3, 4}
>>> s.update([5,6,7])

>>> s.update({8,9})
>>> s   # pssing set
{1, 2, 3, 4, 5, 6, 7, 8, 9}

>>> s.update((9,10))
>>> s   # passing tuple
{1, 2, 3, 4, 5, 6, 7, 8, 9, 10}


>>> s.update(10)
TypeError: 'int' object is not iterable

‘set.remove()’

The remove() method is used to remove a specific element from the set. If the element is not found, it raises a KeyError.

>>> s = {1,2,3,4,5}

>>> s.remove(3)
>>> s
{1, 2, 4, 5}

>>> s.remove(6)
KeyError: 6
# Trying to remove an element that does not exist raises an error

‘set.discard()’

The discard() method is similar to remove(), but it does not raise an error if the element does not exist in the set. This makes it a safer option if you’re unsure whether the element is in the set.

>>> s = {1,2,3,4,5}

>>> s.discard(5)
>>> s
{1, 2, 3, 4}

>>> s.discard(10)
>>> s
{1, 2, 3, 4}

Set Operations

Python provides a variety of operations to perform set-related tasks:

• Union (|) : set1 | set2 Combines two sets, returning all unique elements from both sets.
• Intersection (&) : set1 - set2 Returns only the elements that are present in both sets.
• Difference (-) : set1 - set2 Returns the elements that are in the first set but not in the second set.
• Symmetric Difference (^) : set1 ^ set2 Returns elements that are in either of the sets, but not in both.

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

# Intersection: Elements present in both sets
>>> a & b
{3}

# Union: All unique elements from both sets
>>> a | b
{1, 2, 3, 4, 5}

# Difference: Elements in 'a' but not in 'b'
>>> a - b
{1, 2}

# Difference: Elements in 'b' but not in 'a'
>>> b - a
{4, 5}

# Symmetric Difference: Elements in either 'a' or 'b', but not both
>>> a ^ b
{1, 2, 4, 5}