Python set.update Method: Usage and Examples

A permission set receives multiple new capabilities at once.

What You Need to Understand

set.update(*others) adds all elements from one or more iterables into an existing set. Unlike add(), it consumes the iterables and inserts their individual elements.

When to Use It

A permission set receives multiple new capabilities at once.

Step-by-Step Python Example

permissions = {"read"}
result = permissions.update(["write", "export"], {"admin"})
print(sorted(permissions))
print(result)

How the Example Works

All three new strings are added and result is None, because the set was mutated.

Example Output

['admin', 'export', 'read', 'write']
None
[1, 2, 3]

A Second Example

Compare this smaller variation with the main example, then experiment with your own values.

items = {1}
items.update((2, 3))
print(sorted(items))

Important Behavior and Edge Cases

update("abc") inserts the individual characters, not the complete string. Use add("abc") to add one string member.

Try It Yourself

Update a set with a tuple of numeric IDs.

Common Beginner Mistakes

update("abc") inserts the individual characters, not the complete string. Use add("abc") to add one string member.
Using the wrong collection method for this operation without checking whether it mutates the object, returns a result, or raises on missing data.

Key Takeaways

set.update(*others) adds all elements from one or more iterables into an existing set.
All three new strings are added and result is None, because the set was mutated.
update("abc") inserts the individual characters, not the complete string.