arcane-typing

This package provides advanced typing patterns for Python projects that use ty.

Usage

Add arcane-typing as a dependency to your project:

uv add arcane-typing

Use one of its typing features in your code, for example:

from arcane_typing import hasattr_of_type

def get_name(obj: object) -> str:
    if hasattr_of_type(obj, "name", str):
        return obj.name.upper()
    else:
        return "<unknown>"

Use ty to type-check your code:

uv add --dev ty  # If you are not already using it

uv run ty check

Features

Core utilities

Tests

• TypeOf[expr] can be used to obtain ty's inferred type for an expression in a type annotation or type alias.
• Top[T] can be used to refer to the top-materialization of T.
• Bottom[T] can be used to refer to the bottom-materialization of T.

TypedDict features

Tests

• TypeOf[Keys[T]] gives a union of string literals for the keys that can appear in a TypedDict T.

Type Narrowing

Tests

• hasattr_of_type(obj, "name", T) narrows obj.name to type T if the attribute exists and if it is an instance of T (which can be a class or a union of classes)
• is_sequence_of(obj, T) checks that obj is a sequence and that every element is an instance of T (which can be a class or a union of classes). It narrows obj to Sequence[T] on success.

Development

Use uv to run the following development tasks:

# Linting and formatting
uv run ruff check
uv run ruff format --check

# Type checking
TY_UV=scripts uv run ty check

# Markdown tests
uv run mdtest.py