Python Sets & Sets Programs

Sets in Python:

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·      A Set is an unordered collection data type that is iterable, mutable, and has no duplicate elements.

·      Python’s set class represents the mathematical notion of a set.

·      The major advantage of using a set, as opposed to a list, is that it has a highly optimized method for checking whether a specific element is contained in the set.

·      This is based on a data structure known as a hash table.

·      However, the set itself is mutable. We can add or remove items from it.

·      To create a set, we use the set() function.

How to create a set?

·      A set is created by placing all the items (elements) inside curly braces {}, separated by comma or by using the built-in function set().

·      It can have any number of items and they may be of different types (integer, float, tuple, string etc.).

·      But a set cannot have a mutable element, like list, set or dictionary, as its element.

Examples:

# Set of integers

my_set = {1, 2, 3}

print(my_set)

# Set of mixed datatypes

my_set = {1.0, "Hello", (1, 2, 3)}

print(my_set)

# Set do not have duplicates

# Output: {1, 2, 3, 4}

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

print(my_set)

# Set cannot have mutable items

# here [3, 4] is a mutable list

# If you uncomment line #12,

# this will cause an error.

# TypeError: unhashable type: 'list'

#my_set = {1, 2, [3, 4]}

# We can make set from a list

# Output: {1, 2, 3}

my_set = set([1,2,3,2])

print(my_set)

#Example of set
groceries = {'cereal','milk','starcrunch','beer','duct tape','lotion','beer'}
print(groceries)

if 'milk' in groceries:
    print("You already have milk hoss!")
else:
    print("Oh yes you need milk!")

NOTE: Creating an empty set is a bit tricky.

Empty curly braces {} will make an empty dictionary in Python. To make a set without any elements we use the set() function without any argument.

# initialize a with {}

a = {}

# check data type of a

# Output: <class 'dict'>

print(type(a))

# initialize a with set()

a = set()

# check data type of a

# Output: <class 'set'>

print(type(a))

Frozen Sets

Frozen sets are immutable objects that only support methods and operators that produce a result without affecting the frozen set or sets to which they are applied.

# Python program to demonstrate differences

# between normal and frozen set

# Same as {"a", "b","c"}

normal_set = set(["a", "b","c"])

# Adding an element to normal set is fine

normal_set.add("d")

print("Normal Set")

print(normal_set)

# A frozen set

frozen_set = frozenset(["e", "f", "g"])

print("Frozen Set")

print(frozen_set)

# Uncommenting below line would cause error as

# we are trying to add element to a frozen set

# frozen_set.add("h")

Output:

======

Normal Set

set(['a', 'c', 'b', 'd'])

Frozen Set

frozenset(['e', 'g', 'f'])

Methods for Sets:

==============

1. add(x) Method: Adds the item x to set if it is not already present in the set.

people = {"Jay", "Idrish", "Archil"}

people.add("Daxit")

-> This will add Daxit in people set.

2. union(s) Method: Returns a union of two set.Using the ‘|’ operator between 2 sets is the same as writing set1.union(set2)

people = {"Jay", "Idrish", "Archil"}

vampires = {"Karan", "Arjun"}

population = people.union(vampires)

ALITER

population = people|vampires

-> Set population set will have components of both people and vampire

3. intersect(s) Method: Returns an intersection of two sets.The ‘&’ operator comes can also be used in this case.

victims = people.intersection(vampires)

-> Set victims will contain the common element of people and vampire

4. difference(s) Method: Returns a set containing all the elements of invoking set but not of the second set. We can use ‘-‘ operator here.

safe = people.difference(vampires)

ALITER

safe = people – vampires

-> Set safe  will have all the elements that are in people but not vampire

5. clear() Method: Empties the whole set.

victims.clear()

-> Clears victim set

However there are two major pitfalls in Python sets:

1.   The set doesn’t maintain elements in any particular order.

2.   Only instances of immutable types can be added to a Python set.

Operators for Sets

Sets and frozen sets support the following operators:

key in s           # containment check

key not in s    # non-containment check

s1 == s2         # s1 is equivalent to s2

s1 != s2         # s1 is not equivalent to s2

s1 <= s2        # s1is subset of s2

s1 < s2         # s1 is proper subset of s2

s1 >= s2      # s1is superset of s2

s1 > s2        # s1 is proper superset of s2

s1 | s2         # the union of s1 and s2

s1 & s2      # the intersection of s1 and s2

s1 – s2       # the set of elements in s1 but not s2

s1 ˆ s2       # the set of elements in precisely one of s1 or s2

Code Snippet to illustrate all Set operations in Python

# Python program to demonstrate working# of # Set in Python # Creating two sets set1 = set() set2 = set() # Adding elements to set1 for i in range(1, 6):     set1.add(i) # Adding elements to set2 for i in range(3, 8):     set2.add(i) print("Set1 = ", set1) print("Set2 = ", set2) print("\n") # Union of set1 and set2 set3 = set1 | set2# set1.union(set2) print("Union of Set1 & Set2: Set3 = ", set3) # Intersection of set1 and set2 set4 = set1 & set2# set1.intersection(set2) print("Intersection of Set1 & Set2: Set4 = ", set4) print("\n") # Checking relation between set3 and set4 if set3 > set4: # set3.issuperset(set4)     print("Set3 is superset of Set4") elif set3 < set4: # set3.issubset(set4)     print("Set3 is subset of Set4") else : # set3 == set4     print("Set3 is same as Set4") # displaying relation between set4 and set3 if set4 < set3: # set4.issubset(set3)     print("Set4 is subset of Set3")     print("\n") # difference between set3 and set4 set5 = set3 - set4 print("Elements in Set3 and not in Set4: Set5 = ", set5) print("\n") # checkv if set4 and set5 are disjoint sets if set4.isdisjoint(set5):     print("Set4 and Set5 have nothing in common\n") # Removing all the values of set5 set5.clear() print("After applying clear on sets Set5: ") print("Set5 = ", set5) Output: ('Set1 = ', set([1, 2, 3, 4, 5])) ('Set2 = ', set([3, 4, 5, 6, 7])) ('Union of Set1 & Set2: Set3 = ', set([1, 2, 3, 4, 5, 6, 7])) ('Intersection of Set1 & Set2: Set4 = ', set([3, 4, 5])) Set3 is superset of Set4 Set4 is subset of Set3 ('Elements in Set3 and not in Set4: Set5 = ', set([1, 2, 6, 7])) Set4 and Set5 have nothing in common After applying clear on sets Set5: ('Set5 = ', set([]))

Basic Types in Python in a Line

========================
a=10                       #int
b="hello"              #str
c=2.5                      #float
e=bytearray()       #bytearray
f=(1,2,3)                #tuple
g=[1,2,3]               #list
h={1,2,3}              #set
i={}                       #dict
j=b"sample"       #bytes
k=None               #empty
=========================

Question : What is the difference between a set and a dictionary?

A set is an unordered data type which has no duplicate items inside it. a dictionary arranges items as {"key": "value"} pairs. sets are very handy when comparisons are to be made since sets handle data in a very controlled way as they dont allow duplicates, but dicts are useful when we want to store a bunch a data inside a single key, for example, all the cources offered in a school could be values stored inside the key which could be the school name, this is useful if we were handling large amount data that involved working with all the schools of a region.

Sets Related Programs:

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1. Program to Count the Number of Vowels Present in a String using Sets:

s=input("Enter string:")

count = 0

vowels = set("aeiou")

for letter in s:

    if letter in vowels:

        count += 1

print("Count of the vowels is:")

print(count)

Output:

======

1:

Enter string:Hello world

Count of the vowels is:

3

2:

Enter string: manish

Count of the vowels is:

2

2. Program to Check Common Letters in Two Input Strings.

s1=input("Enter first string:")

s2=input("Enter second string:")

a=list(set(s1)&set(s2))

print("The common letters are:")

for i in a:

    print(i)

Output:

======

1:

Enter first string: manish

Enter second string: bidsar

The common letters are:

a

i

s

2:

Enter first string:Test string

Enter second string:checking

The common letters are:

i

e

g

n

3.  Program that displays which Letters are in the First String but not in the Second

s1=input("Enter first string:")

s2=input("Enter second string:")

a=list(set(s1)-set(s2))

print("The letters are:")

for i in a:

    print(i)

Output:

======

1:

Enter first string: manish

Enter second string: bidsar

The letters are:

n

h

m

2:

Enter first string:Python

Enter second string:Programming language

The letters are:

y

h

t

4.  Program that Displays which Letters are Present in Both the Strings

s1=input("Enter first string:")

s2=input("Enter second string:")

a=list(set(s1)|set(s2))

print("The letters are:")

for i in a:

    print(i)

Output:

======

1:

Enter first string:hello

Enter second string:world

The letters are:

e

d

h

l

o

r

w

2:

Enter first string:test

Enter second string:string

The letters are:

e

g

i

n

s

r

t

5. Program that Displays which Letters are in the Two Strings but not in Both

s1=input("Enter first string:")

s2=input("Enter second string:")

a=list(set(s1)^set(s2))

print("The letters are:")

for i in a:

    print(i)

Output:

======

1:

Enter first string: manish

Enter second string: bidsar

The letters are:

n

b

m

d

h

r

2:

Enter first string:hello

Enter second string:world

The letters are:

e

d

h

r

w

For a Quick Recap Watch the Below Video :