Python Fundamentals - Python Sets

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Python Fundamentals - Python Sets

What is Set?

Set in Python is a data structure equivalent to sets in mathematics. It may consist of various elements; the order of elements in a set is undefined.

Python set is a collection which is unordered and unindexed. In Python, sets are written with curly brackets.

Example
Create a Set:

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

Operations on Python Sets

1) Access Items

We cannot access items in a set by referring to an index, since sets are unordered the items has no index.
But we can loop through the set item

Example 1:

Loop through the set, and print the all values

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

for x in fruits:
print(x)

Example 2:

Check if "banana" is present in the set:

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

print("banana" in fruits)

Note: It will print True/False like result

2) Change Items

Once a set is created, we cannot change its items, but we can add new items.

3) Add Items

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

ii) To add more than one item to a set use the update() method.

Example 1:

Add an item to a set, using the add() method:

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

fruits.add("orange")

print(fruits)

Example 2:

Add multiple items to a set, using the update() method:

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

fruits.update(["orange", "mango", "grapes"])

print(fruits)

4) Get the Length of a Set

To determine how many items a set has, use the len() method.

Example
Get the number of items in a set:

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

print(len(fruits))

5) Remove Item

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

Example 1:

Remove "banana" by using the remove() method:

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

fruits.remove("banana")

print(fruits)
-----------------------------------
Example 2:

Remove "banana" by using the discard() method:

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

fruits.discard("banana")

print(fruits)

Note: If the item to remove does not exist, discard() will NOT raise an error.
-------------------------
Example 3:

Remove the last item by using the pop() method:

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

x = fruits.pop()

print(x)

print(fruits)

Note: Sets are unordered, so when using the pop() method, you will not know which item that gets removed.
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Example 4:

The clear() method empties the set:

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

fruits.clear()

print(fruits)
-----------------------------
Example 5:

The del keyword will delete the set completely:

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

del fruits

print(fruits)

Note: It will show error

6) Join Two Sets

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

You can use the union() method that returns a new set containing all items from both sets, or the update() method that inserts all the items from one set into another:

Example 1:

The union() method returns a new set with all items from both sets:

set1 = {"a", "b" , "c"}
set2 = {1, 2, 3}

set3 = set1.union(set2)
print(set3)
--------------------------
Example 2:

The update() method inserts the items in set2 into set1:

set1 = {"a", "b" , "c"}
set2 = {1, 2, 3}

set1.update(set2)
print(set1)