Python · Theory

Python Sets

Theory

35/268

Python Sets

A set stores unique items with no guaranteed order. {1, 2, 2, 3} becomes {1, 2, 3}. Membership in is fast on average. Union |, intersection &, difference -. Empty set is set() — {} is an empty dict. That {} trap fails more interviews than the algebra.

frozenset is the immutable version. Use a set when duplicates must disappear: unique emails, unique roll numbers. Don’t use a set when order matters — print order can surprise you.

Python Sets — output — {1, 2, 3}, then union {1,2,3,4}, then intersection {3}.

Diagram

{1, 2, 2, 3}
         │ unique
         ▼
      {1, 2, 3}

Exam tip

{} is dict; set() is empty set.

Example

# Sets
a = {1, 2, 2, 3}
b = {3, 4}
print(a)
print(a | b)
print(a & b)

Python Sets — output: {1, 2, 3}, then union {1,2,3,4}, then intersection {3}.

Short notes

DefUnique, unordered.
RuleEmpty = set(), not {}.
Remember| & -.

Python · Theory

Python Sets

← All stacks

Theory

35/268

Python Sets

frozenset is the immutable version. Use a set when duplicates must disappear: unique emails, unique roll numbers. Don’t use a set when order matters — print order can surprise you.

Python Sets — output — {1, 2, 3}, then union {1,2,3,4}, then intersection {3}.

Diagram

{1, 2, 2, 3}
         │ unique
         ▼
      {1, 2, 3}

Exam tip

{} is dict; set() is empty set.

Example

# Sets
a = {1, 2, 2, 3}
b = {3, 4}
print(a)
print(a | b)
print(a & b)

Python Sets — output: {1, 2, 3}, then union {1,2,3,4}, then intersection {3}.

Short notes

DefUnique, unordered.
RuleEmpty = set(), not {}.
Remember| & -.

Python Sets

Example

Short notes

Questions

Python Sets

Example

Short notes

Questions