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Set Methods >

In Python, a set is a collection of unique items. You can think of a set like a box that only holds distinct items. If you try to add the same item again, it won’t be stored.

Key Features of Sets:

  • Unique: No duplicates allowed.
  • Unordered: The items don’t follow any specific order.
  • Mutable: You can change the set after it’s created.

Creating Sets

To create a set, you use curly braces {} or the set() function.

Example 1: Creating a Set Using Curly Braces

fruits = {"apple", "banana", "cherry"}
print(fruits)

Output:

{'banana', 'apple', 'cherry'}

Notice that the order of the items may vary when printed. That’s because sets are unordered.

Example 2: Creating a Set Using the set() Function

numbers = set([1, 2, 3, 4, 5])
print(numbers)

Output:

{1, 2, 3, 4, 5}

Adding Items to a Set

You can add new items to a set using the add() method.

Example 3: Adding an Item

fruits = {"apple", "banana", "cherry"}
fruits.add("orange")
print(fruits)

Output:

{'banana', 'apple', 'cherry', 'orange'}

Removing Items from a Set

To remove an item from a set, use the remove() or discard() method.

  • remove() will throw an error if the item does not exist.
  • discard() will not throw an error if the item does not exist.

Example 4: Removing an Item with remove()

fruits = {"apple", "banana", "cherry"}
fruits.remove("banana")
print(fruits)

Output:

{'apple', 'cherry'}

Example 5: Removing an Item with discard()

fruits = {"apple", "banana", "cherry"}
fruits.discard("orange")  # No error even though 'orange' is not in the set
print(fruits)

Output:

{'banana', 'apple', 'cherry'}

Set Operations

Sets also support various operations that allow you to combine or compare sets.

Union: Combining Two Sets

You can combine two sets using the | operator or the union() method.

Example 6: Union of Sets

fruits = {"apple", "banana", "cherry"}
more_fruits = {"orange", "grape", "apple"}
combined_fruits = fruits | more_fruits
print(combined_fruits)

Output:

{'banana', 'grape', 'cherry', 'orange', 'apple'}

Notice that the duplicate “apple” is only stored once in the result.

Intersection: Finding Common Items

The intersection of two sets gives you the items that are in both sets. You can use the & operator or the intersection() method.

Example 7: Intersection of Sets

fruits = {"apple", "banana", "cherry"}
more_fruits = {"orange", "grape", "apple"}
common_fruits = fruits & more_fruits
print(common_fruits)

Output:

{'apple'}

Difference: Items Only in One Set

The difference of two sets gives you the items that are in the first set but not in the second. You can use the - operator or the difference() method.

Example 8: Difference of Sets

fruits = {"apple", "banana", "cherry"}
more_fruits = {"orange", "grape", "apple"}
exclusive_fruits = fruits - more_fruits
print(exclusive_fruits)

Output:

{'banana', 'cherry'}

Why Use Sets?

Sets are useful when you want to:

  • Ensure that a collection has no duplicates.
  • Perform mathematical set operations like union, intersection, and difference.
  • Check membership (whether an item is in the set) efficiently.
< Dict Methods
Set Methods >