set.update()

set.update(*others)

Returns: None · Updated March 15, 2026 · Set Methods

sets methods mutation set-operations

The update() method adds all elements from one or more iterables to a set. Unlike methods like union() that return a new set, this method modifies the original set directly. It accepts any number of iterables as arguments and silently ignores duplicate values.

Syntax

set.update(*others)

Parameters

Parameter	Type	Description
`*others`	iterable	Any number of iterables (sets, lists, tuples, strings, dicts, etc.) whose elements will be added to the set.

Examples

Basic usage

Add elements from another set:

s = {1, 2, 3}
s.update({4, 5})
print(s)  # {1, 2, 3, 4, 5}

From a list or tuple

You can add elements from any iterable:

s = {"a", "b"}
s.update(["c", "d"])
print(s)  # {"a", "b", "c", "d"}

s.update(("e", "f"))
print(s)  # {"a", "b", "c", "d", "e", "f"}

Using multiple arguments

Add elements from several iterables at once:

s = {1}
s.update([2, 3], (4, 5), {6})
print(s)  # {1, 2, 3, 4, 5, 6}

This is equivalent to calling update() multiple times or using the |= operator.

With a dictionary

When updating with a dictionary, only the keys are added:

s = {"a"}
s.update({"b": 1, "c": 2})
print(s)  # {"a", "b", "c"}

Duplicates are ignored

Only unique elements are added:

s = {1, 2}
s.update([2, 3, 3, 3])
print(s)  # {1, 2, 3}

Using the |= operator

The |= operator is equivalent to update():

s = {1, 2}
s |= {3, 4}
print(s)  # {1, 2, 3, 4}

Common Patterns

Merging collections

A common pattern is merging multiple data sources:

initial = {"user1", "user2"}
new_users = ["user3", "user4"]
removed_users = {"user1"}

initial.update(new_users)
for u in removed_users:
    initial.discard(u)
print(initial)  # {"user2", "user3", "user4"}

Building a set from user input

Collect unique values from various input sources:

tags = set()
tags.update(input("Enter tags: ").split())
tags.update(input("More tags: ").split())
print(sorted(tags))

Performance

The update() method:

Time complexity: O(len(others)) where others is the total number of elements across all iterables
Space complexity: O(n) for the elements being added
Each element is hashed once, making lookups efficient

For combining sets without mutating the original, use set.union() instead.

Return Value

This method returns None — it modifies the set in place. This is different from union() which returns a new set.