Python Sets

 

Sets

Unordered collection of items.

Every set element is

• Unique (no duplicates)
• Must be immutable

Creating a Set

• Created by enclosing elements within {curly} brackets.
• Each item is separated by a comma.

Code

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a = 2

set_a = {5, "Six", a, 8.2}

print(type(set_a))

print(set_a)

PYTHON

Output

<class 'set'>

{8.2, 2, 'Six', 5}

Need not be in the same order as defined.

No Duplicate Items

Sets contain unique elements

Code

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set_a = {"a", "b", "c", "a"}

print(set_a)

PYTHON

Output

{'b', 'a', 'c'}

Immutable Items

Set items must be immutable. As List is mutable, Set cannot have list as an item.

Code

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set_a = {"a", ["c", "a"]}

print(set_a)

PYTHON

Output

TypeError: unhashable type: 'list'

Creating Empty Set

We use

set()

to create an empty set.

Code

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set_a = set()

print(type(set_a))

print(set_a)

PYTHON

Output

<class 'set'>

set()

Converting to Set

set(sequence)

takes any sequence as argument and converts to set, avoiding duplicates

List to Set

Code

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set_a = set([1,2,1])

print(type(set_a))

print(set_a)

PYTHON

Output

<class 'set'>

{1, 2}

String to Set

Code

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set_a = set("apple")

print(set_a)

PYTHON

Output

{'l', 'p', 'e', 'a'}

Tuple to Set

Code

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set_a = set((1, 2, 1))

print(set_a)

PYTHON

Output

{1, 2}

Accessing Items

As sets are unordered, we cannot access or change an item of a set using

• Indexing
• Slicing

Code

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set_a = {1, 2, 3}

print(set_a[1])

print(set_a[1:3])

PYTHON

Output

TypeError: 'set' object is not subscriptable

Adding Items

set.add(value)

adds the item to the set, if the item is not present already.

Code

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set_a = {1, 3, 6, 2, 9}

set_a.add(7)

print(set_a)

PYTHON

Output

{1, 2, 3, 6, 7, 9}

Adding Multiple Items

set.update(sequence)

adds multiple items to the set, and duplicates are avoided.

Code

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set_a = {1, 3, 9}

set_a.update([2, 3])

print(set_a)

PYTHON

Output

{2, 1, 3, 9}

Removing Specific Item

set.discard(value)

takes a single value and removes if present.

Code

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set_a = {1, 3, 9}

set_a.discard(3)

print(set_a)

PYTHON

Output

{1, 9}

set_a.remove(value)

takes a value and remove if it present or raise an error.

Code

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set_a = {1, 3, 9}

set_a.remove(5)

print(set_a)

PYTHON

Output

KeyError: 5

Operations on Sets

You can perform the following operations on Sets

• clear()
• len()
• Iterating
• Membership Check