dependent-types 0.0.0

Dependent types for Python

dependent-types

Dependent types for Python.

Installation

python3 -m pip install dependent-types

Abstract

• Make illegal states unrepresentable.
• Abuse __instancecheck__ and type-guards.

Usage

Builtin types

dept.datetime

• TZAware
• TZNaive

dept.numeric

• Natural
• NegativeInt
• Portion

dept.sized

• NonEmpty
• Empty

Creating dependent types

To create new dependent types, subclass dept.base.Dependent and define a __instancecheck__ method:

from typing import Any
from dept.base import Dependent


class StartsWithHello(str, Dependent[str]):
    def __instancecheck__(self, instance: Any) -> bool:
        return isinstance(instance, str) and instance.startswith("Hello")


isinstance("Hello there", StartsWithHello)  # True
isinstance("Hi there", StartsWithHello)  # False

Checkout out the dacite example for how to create dataclasses with rich dependently typed fields without duplicating type definitions or losing parsed information.