A set is a collection which is unordered, unchangeable*, and unindexed. Sets do not allow duplicate values.

*Note: Set items are unchangeable, but you can remove items and add new items.

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1. Create set

Sets are written with curly brackets {}.

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

Because sets are unordered, you cannot be sure in which order the items will appear.

No Duplicates Allowed

If you try to create a set with duplicate items, the duplicates will be ignored:

thisset = {"apple", "banana", "cherry", "apple"}
print(thisset) # {'banana', 'cherry', 'apple'}

Note: The values True and 1 are considered the same value in sets, and are treated as duplicates. False and 0 are also considered the same.

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2. Add items

To add one item to a set use the add() method.

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

To add items from another set into the current set, use the update() method.

thisset = {"apple", "banana", "cherry"}
tropical = {"pineapple", "mango", "papaya"}
thisset.update(tropical)

The object in the update() method does not have to be a set, it can be any iterable object (tuples, lists, dictionaries etc.).

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3. Remove items

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

• remove(): If the item to remove does not exist, remove() will raise an error.
• discard(): If the item to remove does not exist, discard() will NOT raise an error.

thisset = {"apple", "banana", "cherry"}
thisset.remove("banana")
thisset.discard("apple")

You can also use the pop() method, but because sets are unordered, pop() will remove a random item. The return value of the pop() method is the removed item.

x = thisset.pop() # Removes a random item
thisset.clear()   # Empties the set

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4. Loop through set

You can loop through the set items by using a for loop.

thisset = {"apple", "banana", "cherry"}

for x in thisset:
    print(x)

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5. Join sets

There are several ways to join two or more sets in Python.

• union() and update(): Both will combine sets and exclude any duplicate items.

  set1 = {"a", "b" , "c"}
  set2 = {1, 2, 3}
  set3 = set1.union(set2) # Returns a new set

• intersection() or intersection_update(): Keep ONLY the duplicates (items that exist in both sets).

  set1 = {"apple", "banana", "cherry"}
  set2 = {"google", "microsoft", "apple"}
  set3 = set1.intersection(set2) # {'apple'}

• symmetric_difference(): Keep all items EXCEPT the duplicates.

  set1 = {"apple", "banana", "cherry"}
  set2 = {"google", "microsoft", "apple"}
  set3 = set1.symmetric_difference(set2) # {'banana', 'cherry', 'google', 'microsoft'}

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6. Set methods

Python has a set of built-in methods that you can use on sets.

Method	Description
add()	Adds an element to the set
clear()	Removes all the elements from the set
copy()	Returns a copy of the set
difference()	Returns a set containing the difference between two or more sets
discard()	Remove the specified item
issubset()	Returns whether another set contains this set or not
issuperset()	Returns whether this set contains another set or not