Convert a List to Set in Python

This article will discuss different ways to convert a list to a set in Python.

Table Of Contents

• Convert a List to a Set using the default constructor
• Convert a List to a set using curly brackets
• Convert a List to a set using iteration
• Convert a List to a set using set comprehension

Suppose we have a list,

[110, 100, 89, 100, 89, 91, 92, 93, 91, 97, 96, 96, 100, 110]

Now we want to convert this list to a set like this,

{96, 97, 100, 110, 89, 91, 92, 93}

Some of the essential points to note here are,

• A set in Python contains unique elements. So when we convert a list to Python, duplicate elements will not be added to the Set.
• A set uses hashing internally to filter out duplicate elements. So after converting a list into a set, the order of elements in Set will be different from the list.

Let’s see how to convert a list to set in Python.

Convert a List to a Set using the default constructor

We can pass the list object to Set () constructor to create a Set populated with list contents. For example,

# Create a list of integers
numbers = [110, 100, 89, 100, 89, 91, 92, 93, 91, 97, 96, 96, 100, 110]

# Convert a List to a Set
setOfNumbers = set(numbers)

print(setOfNumbers)

Output:

{96, 97, 100, 110, 89, 91, 92, 93}

It converted the list to a set. Duplicate elements from list were not added to the Set, and also, the order of elements in Set is different from the list.

Convert a List to a set using curly brackets

We can use the * operator with list to unpack the list elements into positional arguments and pass them to the curly brackets i.e. {}. It will create a set object from the list contents. For example,

# Create a list of integers
numbers = [110, 100, 89, 100, 89, 91, 92, 93, 91, 97, 96, 96, 100, 110]

# Convert a List to a Set
setOfNumbers = {*numbers}

print(setOfNumbers)

Output:

{96, 97, 100, 110, 89, 91, 92, 93}

It converted the list to a set. Duplicate elements from list were not added to the set, and also, the order of elements in set is different from the list.

Convert a List to a set using iteration

We can initialize an empty set. Then iterate over the list elements using for loop and add them to the set one by one. For example,

# Create a list of integers
numbers = [110, 100, 89, 100, 89, 91, 92, 93, 91, 97, 96, 96, 100, 110]

# Convert a List to a Set
setOfNumbers = set()
for item in numbers:
    setOfNumbers.add(item)

print(setOfNumbers)

Output:

{96, 97, 100, 110, 89, 91, 92, 93}

This approach has the advantage of filtering out elements if we want based on conditions. For example, let’s convert the list to set but include only greater than 95. For example,

# Create a list of integers
numbers = [110, 100, 89, 100, 89, 91, 92, 93, 91, 97, 96, 96, 100, 110]

# Convert a List to a Set but add 
# items greater than 95 only
setOfNumbers = set()
for item in numbers:
    if item > 95:
        setOfNumbers.add(item)

print(setOfNumbers)

Output:

{96, 97, 100, 110}

This added unique items greater than 95 to the set.

Convert a List to a set using set comprehension

Initialize an empty set. Then iterate over the list elements using set comprehension and add items to set one by one. For example,

# Create a list of integers
numbers = [110, 100, 89, 100, 89, 91, 92, 93, 91, 97, 96, 96, 100, 110]

# Convert a List to a Set
setOfNumbers = {item for item in numbers}

print(setOfNumbers)

Output:

{96, 97, 100, 110, 89, 91, 92, 93}

We can skip certain elements based on conditions while converting the list to set. For example, let’s convert the list to set but include only greater than 95. For example,

# Create a list of integers
numbers = [110, 100, 89, 100, 89, 91, 92, 93, 91, 97, 96, 96, 100, 110]

# Convert a List to a Set but add 
# items greater than 95 only
setOfNumbers = {item for item in numbers if item > 95}

print(setOfNumbers)

Output:

{96, 97, 100, 110}

This added unique items greater than 95 to the set.

Summary:

We learned different ways to convert a list to set in Python.