Interview Q&A / Python

1. What is the difference between __str__ and __repr__ in Python?

   __str__ gives a readable description meant for users and is used by print() and str(). __repr__ gives an unambiguous description meant for developers, ideally looking like code that recreates the object. If only __repr__ exists, print falls back to it.

   BeginnerQuick answer1 min read
2. How do you make your own class work with +, len() and indexing in Python?

   Implement the matching dunder methods: __add__ for +, __len__ for len(), and __getitem__ for obj[i]. Python translates the syntax into calls to these methods, so no inheritance from built-in types is needed.

   IntermediateQuick answer1 min read
3. Why must you define __hash__ when you define __eq__ for objects used in sets or as dict keys?

   Objects that compare equal must have the same hash, or sets and dicts will treat them as different. Defining __eq__ without __hash__ sets __hash__ to None, so the class becomes unhashable. Base the hash on the same fields that __eq__ compares.

   AdvancedQuick answer1 min read