ihoop 0.1.4

Abstract/Final Patterns in Python

ihoop

Strict, immutable Abstract/Final classes

Do you like python, but wish it is was more like Julia? Do like Julia, but wish it was a language other people used? Did you read Design Patterns: Elements of Reusable Object-Oriented Software, but wish you didn't?

Meet ihoop: a tiny library that turns plain Python classes into frozen, Abstract/Final instances. Drop in Strict as a base class and get:

• Immutability by default: once __init__ finishes, your objects are read-only.
• Abstract or Final:
  • Abstract classes: can be subclassed, but cannot be instantiated.
  • Concrete classes: can be instantiated, but cannot be subclassed.
• Abstract attributes, not just methods: Declare with AbstractAttribute[T]; subclasses must supply (via type hints) a real value.
• Abstract class variables: Declare with AbstractClassVar[T]; subclasses must supply a value, which becomes immutable.
• No dependencies: pure Python.

This package was largely copied inspired by equinox's strict=True flag. For more information see https://docs.kidger.site/equinox/pattern/.

Why is it called ihoop? Because (i) (h)ate (o)bject (o)riented (p)rogramming 😉

Example

from ihoop import Strict, AbstractAttribute, AbstractClassVar

class AbstractAnimal(Strict):
    name: AbstractAttribute[str]
    species: AbstractClassVar[str]

class Dog(AbstractAnimal):
    name: str
    species = "Canis familiaris"

    def __init__(self, name: str):
        self.name = name

>>> Dog("Fido").name
'Fido'
>>> Dog.species
'Canis familiaris'
>>> d = Dog("Rex")
>>> d.name = "Max"  # Instance attributes are immutable
AttributeError: Cannot set attribute 'name' on frozen instance of Dog. strict objects are immutable after initialization.
>>> Dog.species = "Something else"  # Class variables are also immutable once resolved
AttributeError: Cannot set frozen class variable 'species' on class 'Dog'. Class variables resolved from abstract requirements are immutable.

Sharp Edges

• It is important to type hint all member variables at the class level. It is very possible to bypass the checking/enforcement of Strict by doing things in the __init__.

Roadmap

• dataclass testing and integration
• abstractclassvar: strictness for class variables
• Package for pypi
• ?