Dunder Methods and Operator Overloading
Explore how to implement Python's special dunder methods to make custom classes act like built-in types. Learn operator overloading, custom string representations, and rich comparisons to write clear, idiomatic Python code that allows objects to participate naturally in expressions, indexing, and iteration.
Python’s syntax is elegant because it is consistent. We use + to add numbers, combine strings, or merge lists. We use len() to size up dictionaries, tuples, or sets. This behavior is not limited to built-in types. It follows a design pattern known as the Python Data Model. By defining special methods with double underscores, known as dunder methods, custom classes can behave like native Python objects. This enables objects to participate directly in expressions, loops, and comparisons.
The delegation pattern
When code uses operators such as + or functions such as len(), Python does not execute the logic directly. Instead, Python searches for a corresponding method defined on the object and invokes it. The operator acts as syntactic sugar that delegates the operation to a corresponding dunder method.
If we write a + b, Python translates it to a.__add__(b). If we write len(a), Python translates it to a.__len__(). To enable this behavior in our classes, we simply implement the corresponding method.
The Vector class: Identity and size
We will use a Vector class (representing mathematical coordinates like x, y ...