Python Sets — Python Technical Interview Questions & Answers

Python Sets

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

Technical Interview Tip: {} is dict; set() is empty set.

Code Examples for Python Sets

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}.

How to Explain Python Sets to an Interviewer

Explain Sets as if you are teaching a junior — definition, then one tiny script.

Unique, unordered. Empty = set(), not {}.

What does the example print, and why?

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

What mistake do freshers make with Sets?

| & -.