Python set - Add the value to a set

You can add an item to a set using add().

s = {'a', 'b'}

s.add('c')

print(s)  # {'c', 'b', 'a'}

A Python set has no order so the result of print() changes at random. This function returns None.

s = {'a', 'b'}

t = s.add('c')

print(s)  # {'c', 'b', 'a'}
print(t)  # None

Add an element that already exists in the Python set

s = {'a', 'b'}

t = s.add('a')

print(s)  # {'b', 'a'}

Adding the value that already exists doesn't change the set.

Union sets in Python

s = {'a', 'b'}
t = {'c', 'd'}

u = s | t

print(u)
# {'d', 'b', 'a', 'c'}

In python, | symbol means set union and more than two sets can be united by |.

s = {'a', 'b'}
t = {'c', 'd'}
u = {'Java', 'Python'}

w = s | t | u

print(w)
# {'Python', 'b', 'a', 'c', 'd', 'Java'}

add() returns None and | returns new set.

update()

s1 = {'a', 'b'}
s2 = {'a', 'b'}

s1.update('c')
s2.update({'c'})

print(s1)  # {'b', 'c', 'a'}
print(s2)  # {'b', 'c', 'a'}

update() can substitute add() in some cases.

Add None

s = {1, 2, 3, 4}

s.add(None)

print(s)  # {1, 2, 3, 4, None}