Python sets are mutable, meaning you can add new items to them after creation. You can use the add() method to add a single item and update() to add multiple items at once.

Python sets allow dynamic insertion of items. You can add:

• A single item using add()
• Multiple items using update()

1. Add a Single Item using add()

languages = {"Python", "Java"}
languages.add("C++")
print(languages)

Output:

{'Python', 'Java', 'C++'}

add() inserts an item only if it's not already in the set.

2. Adding an Existing Item (No Error, No Effect)

languages = {"Python", "Java"}
languages.add("Python")
print(languages)

Output:

{'Python', 'Java'}

No duplicate is added, and Python doesn’t raise an error.

3. Add Multiple Items using update()

languages = {"Python", "Java"}
languages.update(["C++", "JavaScript"])
print(languages)

Output:

{'Python', 'JavaScript', 'C++', 'Java'}

4. Add Items from Another Set

set1 = {"HTML", "CSS"}
set2 = {"JavaScript", "React"}
set1.update(set2)
print(set1)

Output:

{'JavaScript', 'React', 'HTML', 'CSS'}

5. Add Items from a Tuple

tools = {"Git", "Docker"}
tools.update(("Kubernetes", "Ansible"))
print(tools)

Output:

{'Git', 'Docker', 'Kubernetes', 'Ansible'}

6. Add Characters from a String (Character-by-Character)

alphabets = {"a", "b"}
alphabets.update("cde")
print(alphabets)

Output:

{'e', 'b', 'd', 'c', 'a'}

⚠️ Strings are iterables, so update("cde") adds 'c', 'd', and 'e' individually.

7. Add Elements from a List of Mixed Data Types

mixed = {1, 2}
mixed.update([3, "four", (5, 6)])
print(mixed)

Output:

{1, 2, 3, 'four', (5, 6)}

Sets can hold mixed types as long as they’re hashable.

8. Add Elements from Another Set Conditionally

a = {1, 2, 3}
b = {3, 4, 5}
# Add only elements > 3 from b
a.update({x for x in b if x > 3})
print(a)

Output:

{1, 2, 3, 4, 5}

You can use set comprehensions with update() for more control.

Bonus Tip: Immutable Types Only

You can only add immutable (hashable) items like strings, numbers, and tuples. Trying to add a list will raise an error:

items = {1, 2}
items.add([3, 4])  # ❌ ERROR: list is unhashable

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