kanne 2.1.1

a context-aware si-unit registry manager built on pint and pydantic

kanne

kanne

Kanne is a small utility package to help manage unit-aware quantities and a simple registry/context pattern for parsing and validating units using Pint. It provides convenience helpers, validators, and a minimal context manager (Kanne) to make working with Pint registries explicit and testable.

Key ideas:

• Keep unit parsing and validation ergonomic.
• Provide a lightweight context aware registry (Kanne) for libraries.
• Export commonly-used units and small helpers for convenience.

📦 Installation

uv add kanne

⚡ Quick Start

Kanne provides a context manager to manage Pint registries easily.

Fields are typed by physical dimension (Duration, Length, …), not by a fixed unit. A field accepts any unit-bearing value of the right dimension, preserves the unit you gave it, and serializes to an abbreviated pint string that the matching server library parses back. A bare number (no unit) is rejected, and so is a value of the wrong dimension.

from kanne.kanne import Kanne
from kanne import Duration, Length
from kanne.registry import KanneRegistry
from pydantic import BaseModel


class Event(BaseModel):
    duration: Duration   # any time quantity
    extent: Length       # any spatial length


with Kanne(registry=KanneRegistry()):
    event = Event(duration="1500 ms", extent="2.5 um")

    event.model_dump()       # {'duration': '1500 ms', 'extent': '2.5 µm'} — unit preserved
    event.duration.to("s")   # <Quantity(1.5, 'second')>

    Event(duration="3 m", extent="1 m")   # raises — a length is not a duration
    Event(duration=1500, extent="1 m")    # raises — bare numbers are ambiguous

    # arithmetic stays dimensionful
    event.duration + event.extent          # raises — incompatible dimensions