rarg-python-patterns

A small, self-contained collection of reusable Python patterns. The first (and currently only) pattern is a Multiton: an implementation of the Multiton pattern with TTL-based cache expiry, importable from rarg_python_patterns.multiton.

Multiton

A Multiton wraps a factory function and its arguments. The underlying instance is created lazily on first access to .instance and cached, keyed on the (frozen, hashable) factory and arguments. Any Multiton constructed with the same factory and arguments shares the cached instance. Multiton objects are themselves hashable, equality-comparable and pickleable (with pickle, cloudpickle and dill), provided their arguments are too.

Cached instances expire after ttl seconds of inactivity; accessing .instance resets the TTL. Expired entries are swept on every access via a min-heap ordered by expiry time.

from rarg_python_patterns import Multiton


def open_connection(url: str, timeout: float = 1.0) -> Connection:
    ...


# The resource is only created when `.instance` is first accessed.
resource = Multiton(open_connection, "https://www.python.org", timeout=10.0)
response = resource.instance.request("GET", "/foo/bar.html")

# Override the default TTL (300s) per-instance.
resource = Multiton(open_connection, "https://www.python.org").with_args(ttl=60.0)

Installation

pip install rarg-python-patterns

The package has no required runtime dependencies. numpy is an optional dependency: when installed, numpy.ndarray factory arguments are frozen by their bytes, shape and dtype so they can be used as cache keys.

Development

This package uses uv.

uv sync
uv run --group test py.test tests/
uv run --dev pre-commit run -a