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Python Dunder Methods

OOP Core

Magic (Dunder) Methods

Special methods let your classes behave like built-ins. Learn which ones matter most and how to implement them correctly.

Choose the right dunderSupporting equality & hashing

Common methods​

MethodPurpose
__repr__ / __str__Developer vs user-facing display
__len__Support len(obj)
__bool__Truthiness (fallback to __len__)
__iter__ / __next__Iteration
__contains__Membership checks
__eq__, __lt__Comparisons
__enter__, __exit__Context managers

Equality & hashing​

class Currency:
    def __init__(self, code: str):
        self.code = code

    def __eq__(self, other: object) -> bool:
        if not isinstance(other, Currency):
            return NotImplemented
        return self.code == other.code

    def __hash__(self) -> int:
        return hash(self.code)
  • Return NotImplemented when comparison doesn't apply.
  • Update __hash__ whenever you override __eq__.

Next up in your learning path

Encapsulation

Expose safe APIs around dunder functionality.

Design

Slots

Optimize attribute storage for heavy objects.

Performance

Abstract classes

Define interfaces that subclasses must implement.

Advanced