A flock of typed, zero-dependency Python design patterns. Each pattern is a single self-contained pato (a duck you adopt), fully typed, standard library only, and small enough to read in one sitting.
Install
pip install patos
Or copy a single duck. Open its docs page, copy the source from the Source section, and paste it into your own project. No dependency, no version pin, no tool, just one module you own.
The optional PostgreSQL toolkit installs SQLAlchemy, pgvector, and inflection only when a project asks for them.
pip install "patos[sql]"
from patos import sql
Patterns
Creational
| pato | description | docs |
|---|---|---|
Singleton |
one instance per class, __init__ runs once |
docs |
FlyweightMeta |
a metaclass that interns instances by constructor args, build-once and immutable | docs |
Dispatch & selection
| pato | description | docs |
|---|---|---|
Registry |
self-registering class hierarchies via __init_subclass__, with try-each dispatch, select(predicate) and first_available() |
docs |
Strategy |
a named family of interchangeable implementations, with first_available() |
docs |
value_dispatch |
dispatch on a value the way singledispatch dispatches on a type |
docs |
type_dispatch |
dispatch on the first argument's type, the open-type-ladder dual of value_dispatch |
docs |
Structural & lifecycle
| pato | description | docs |
|---|---|---|
Decorator |
a transparent wrapper that forwards everything to the wrapped object but what it overrides | docs |
Pipeline |
a reversible stack of stages, applied forward and unwound in reverse around a core op | docs |
Lifecycle |
a typed state machine that permits only the transitions its table declares | docs |
DerivedCache |
a load-once cache of a derived value keyed by exactly what it depends on | docs |
Command-line
| pato | description | docs |
|---|---|---|
StrFlag |
an enum Flag whose members carry a literal string, OR-combinable and iterable |
docs |
Optional extensions
| namespace | description | docs |
|---|---|---|
sql |
typed SQLModel columns, native PostgreSQL enums, pgvector cosine distance, JSONB reads, and set based SQL helpers | docs |
Example
from patos import Singleton
class Settings(Singleton):
def __init__(self) -> None:
self.debug = False
a = Settings()
a.debug = True
b = Settings() # same object, __init__ did not run again
assert a is b and b.debug
Documentation
Full documentation lives at phvv.me/patos.
Development
- Install:
pip install -e ".[dev]" - Lint:
ruff check . && ruff format --check . - Typecheck:
pyrefly check - Test:
pytest - Docs:
pip install -e ".[docs]" && mkdocs build - Build:
python -m build
1 maintainer
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