Python Sets

Python Sets are another datatype in python which are unordered and eliminates duplication of elements. Items are put one after another enclosed by curly brackets.

Creating empty Sets

• By using curly brackets {} dictionary data-type.
• Also python built-in constructor for sets set() is available.

Important Points about Python Sets:

1) They are an unordered and unindexed collection of datatypes.

2) Duplicate elements are not allowed in sets.

3) Unlike a list, tuples, sets cannot be accessed through index or key.

4) items in the sets are not in sequence they usually change their sequence.

Example: Create an empty Sets

create sets using curly brackets

    a={}

create sets using python built-in set constructor

    b=set()

    print(a)
    print(b)

    #PYTHON OUTPUT
    {}
    set()

Example: Initialize sets using predefined variables.

create sets using curly brackets

    a={
    'sets',
    'change',
    'their',
    'sequence'
    }

create sets using python built-in set constructor

    b=set((
    1,2,3
    ))

    print(a)
    print(b)

    #PYTHON OUTPUT
    {'sequence', 'sets', 'their', 'change'}
    {1, 2, 3}

In the above example, we can see that in sets the sequences(occurrences) of variables change.

Example: Sets Eliminate duplicate items

    a={
        1,2,3,3,2,1
    }

    print(a)#note that duplicate elements has been ommited by sets

    #PYTHON OUTPUT
    {1, 2, 3}

Accessing Sets

Items inside sets cannot be accessed using the index. To access it we have to loop sets using a for-in loop

Example

    a={
    'alice_586',
    'Alice',
    'K',
    '123456',
    }

    for i in a:
        print(i)

    #PYTHON OUTPUT
    K
    123456
    Alice
    alice_586

To verify if a given item exists in Sets

    a={
        'alice_586',
        'Alice',
        'K',
        '123456',
    }


    print('Alice' in a)# returns True
    print('Anthony' in  a)#returns False

    #PYTHON OUTPUT
    True
    False

To count the number of items present in sets use len() method.

    a = {1,2,3,4,}

    print(len(a))

    #PYTHON OUTPUT
    4

To add new items in sets use add() method under sets. But you can add only one value at a time.

    new_set = {'BMW', 'Volvo'}

    new_set.add("Jaguar")

    print(new_set)

    #PYTHON OUTPUT
    {'BMW', 'Volvo', 'Jaguar'}

To add multiple items in sets using update() method under sets.

Syntax

    sets_name.update(another sets variable)

Example

    old_set = {'BMW', 'Volvo'}

    new_set = {'Porsche', 'Bugatti', 'Pagani'}

    old_set.update(new_set)

    print(old_set)

    #PYTHON OUTPUT
    {'Bugatti', 'Volvo', 'BMW', 'Porsche', 'Pagani'}

Note : You cannot update the existing item in sets.

To remove existing item in sets use 'remove()' or 'discard()' method

    new_set = {'Asia', 'Africa', 'Europe'}
    new_set.remove('Asia')
    print(new_set)

    #PYTHON OUTPUT
    {'Europe', 'Africa'}

Note: While using 'remove()' method we must know that if the item doesn't exists. It will give 'KeyError' Error.

Insisted of remove() use discard() method.

    new_set = {'Asia', 'Africa', 'Europe'}
    new_set.remove('Asa')
    print(new_set)

    #PYTHON ERROR OUTPUT
    KeyError: 'Asa'

Using discard() method

    new_set = {'Asia', 'Africa', 'Europe'}
    new_set.discard('Asia')
    print(new_set)

    #PYTHON OUTPUT
    {'Africa', 'Europe'}    

If the item does not exists.

    new_set = {'Asia', 'Africa', 'Europe'}
    new_set.discard('Asi')
    print(new_set)

    #PYTHON OUTPUT
    {'Europe', 'Asia', 'Africa'}

To clear items inside sets use clear() method under sets.

    old_set = {'BMW', 'Volvo'}

    new_set = {'Porsche', 'Bugatti', 'Pagani'}

    old_set.update(new_set)

    old_set.clear()
    print(old_set)

    #PYTHON OUTPUT
    {}

The article is taken from the code learners python sets post