Set in Python

Python Set – Definition & Operations

A Set is a collection of finite elements. It does not maintain any sequence/index and displays elements in a random order. A Set automatically removes duplicates and stores only unique values.

Set can be created using {} or set().

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Syntax of Set

var = {item1, item2, item3}
var = set()

Example

x = {"C","CPP","DS","PHP","Java",".NET"}

# OR
x = set({"C","CPP","DS","PHP","Java",".NET"})

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Example: Set Removes Duplicate Automatically

x = {"C","CPP","DS","PHP","Java",".NET","C","CPP"}

for data in x:
    print(data)

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Adding User Input to a Set

Note: In Python, {} creates a dictionary, not an empty set. So to declare an empty set, always use → set()

x = set()
size = int(input("enter size of set"))

for i in range(0, size):
    item = input("Enter item")
    x.add(item)

print("Set elements are:")

for i in x:
    print(i)

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Where Do We Use Sets?

1. To display random elements
2. To display unique elements

Example: OTP generation can use Sets because it needs random unique values.

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Predefined Methods of Set

x = {"C","CPP","DS","PHP","Java",".NET","C","CPP"}

1) add() – Add an element

x.add("PYTHON")

2) remove() – Remove an element

x.remove("C")

3) max(), min() – Maximum / Minimum element

print(max(x))
print(min(x))

4) sum() – Sum of numeric set elements

print(sum(x))

5) union() – Combine two sets

a = {1,2,3,4}
b = {2,3,7,8,9}
c = a.union(b)

6) intersection() – Common elements

a = {1,2,3,4}
b = {2,3,7,8,9}
c = a.intersection(b)

7) difference() – Elements in A not in B

a = {1,2,3,4}
b = {2,3,7,8,9}
c = a.difference(b)

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Complete Set Example Program

x = {1,12,23,34,45,11,3}
y = {2,3}

x.add(9)
x.remove(1)

print(max(x))
print(min(x))
print(sum(x))

print(x.union(y))
print(y.union(x))

print(x.intersection(y))
print(x.difference(y))

print("data is ")

for data in x:
    print(data)

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Assignments on Set

1. WAP to find the max element in a set without using max().
2. WAP to reverse set elements (display actual random order + reverse order).

Example:

s = {3,11,23,34,56,1,78,19,17,98,1}

s1 = [int] * len(s)
c = 0

for i in s:
    s1[c] = i
    c = c + 1

for i in range(len(s)-1, -1, -1):
    print(s1[i])

3) WAP to display prime elements in Set

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What is Frozenset?

A frozenset is a special type of set that is immutable. You cannot add or remove items.

a = frozenset({1,2,3})

for d in a:
    print(d)