Python Set (Iterate, add, reverse, etc)

A Python set is a set of objects and written with curly braces and comma separators.

s = {'com', 'org', 'net'}

A set can't have a key-value pair like dictionary.

Iterate

s = {1, 2, 7}

for i in s:
    print(i)

# 1
# 2
# 7

Add

s = {1, 2, 7}

s.add(4)

print(s)  # {1, 2, 4, 7}

A set doesn't change if adding the element that already exists.

s = {1, 2, 7}

s.add(2)

print(s)  # {1, 2, 7}

Remove

s = {1, 2, 7}

s.remove(2)

print(s)  # {1, 7}

Python raises the KeyError exception if trying to remove the value that doesn't exist.

s = {1, 2, 7}

s.remove(4)  # KeyError: 4

This remove an item so is the same as remove. But some Python programmers love discard because it doesn't raise the exception.

Empty set

a = {}
b = set()

print(a)  # {}
print(b)  # set()

print(type(a))  # <class 'dict'>
print(type(b))  # <class 'set'>

Only curly braces represents an empty dictionary. An empty set is defined by set function.