Dunder in Python

“Dunder” is short for “double underscore” and is commonly used in programming to refer to special methods and attributes in Python that are surrounded by double underscores on both sides of their name. These dunder methods and attributes have specific meanings and behaviors that provide functionality to classes and objects in Python.

Common Dunder Methods

Object Representation

• __init__: Constructor method, called when an object is created
• __str__: String representation for end users
• __repr__: String representation for developers/debugging

Operator Overloading

• __add__, __sub__, __mul__: Arithmetic operations
• __eq__, __lt__, __gt__: Comparison operations
• __len__: Length/size of object
• __getitem__, __setitem__: Indexing and slicing

Context Managers

• __enter__, __exit__: Used with with statements

Dunder Attributes

• __name__: Name of module, class, or function
• __doc__: Documentation string
• __dict__: Dictionary containing object’s attributes
• __class__: Class to which an object belongs
• __module__: Module in which class is defined

Purpose

Dunder methods enable:

• Customizing object behavior
• Operator overloading
• Context management
• Making objects more Pythonic and intuitive

Related Concepts

• [[Architecture Decision]] — Python’s dunder protocol is a deliberate language-level design decision

Definition based on Python programming practice.