Dunder Methods

In Python, special methods are a set of predefined methods you can use to enrich your classes. They are easy to recognize because they start and end with double underscores, for example init or str.

Dunder methods let you emulate the behavior of built-in types. For example, to get the length of a string you can call len(‘string’). But an empty class definition doesn’t support this behavior out of the box:

class LenSupport:
    def __len__(self):
        return 42

>>> obj = LenSupport()
>>> len(obj)
42

Python Iterators

• Iterators provide a sequence interface to Python objects that’s memory efficient and considered Pythonic. Behold the beauty of the for-in loop!

• To support iteration an object needs to implement the iterator protocol by providing the iter and next dunder methods.

• Class-based iterators are only one way to write iterable objects in Python. Also consider generators and generator expressions.

Python Generators

• Generator functions are syntactic sugar for writing objects that support the iterator protocol. Generators abstract away much of the boilerplate code needed when writing class-based iterators

• The yield statement allows you to temporarily suspend execution of a generator function and to pass back values from it.

• Generators start raising StopIteration exceptions after control flow leaves the generator function by any means other than a yield statement.