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Python Sets

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 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 doesnot 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
{}

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