quacks 0.1.2

Better duck-typing with mypy-compatible extensions to Protocol

If it walks like a duck and it quacks like a duck, then it must be a duck

Better duck-typing with mypy-compatible extensions to Protocol

🎯 Why?

PEP544 gave Python protocols, a way to define duck typing statically. This library gives you some niceties to make common idioms easier.

📦 Installation

pip install quacks

⚠️ For type checking to work with mypy, you’ll need to enable the plugin in your mypy config file:

[mypy]
plugins = quacks.mypy

⭐️ Features

Easy read-only protocols

Defining read-only protocols is great for encouraging immutability and working with frozen dataclasses. Use the readonly decorator:

from quacks import readonly

@readonly
class User(Protocol):
    id: int
    name: str
    is_premium: bool

Without this decorator, we’d have to write quite a lot of cruft, reducing readability:

class User(Protocol):
    @property
    def id(self) -> int: ...
    @property
    def name(self) -> str: ...
    @property
    def is_premium(self) -> bool: ...

Partial protocols (🏗)

(🚧 work in progress 🚧)

What if you only need part of a protocol? Imagine we have several functions who use various properties of User. With partial protocols you can reuse a data ‘shape’ without requiring all attributes.

(exact syntax TBD)

from quacks import q

def determine_discount(u: User[q.id.is_premium]) -> int:
    ...  # access `id` and `is_premium` attributes

def greet(u: User[q.id.name]) -> None:
    ...  # access `id` and `name` attributes

u: User = ...

determine_discount(u)
greet(u)