🦆 Quacks

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

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


pip install quacks

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

plugins = quacks.mypy


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

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):
    def id(self) -> int: ...
    def name(self) -> str: ...
    def is_premium(self) -> bool: ...

Partial protocols (work in progress)

What if you want to reuse parts of a protocol?
Imagine we have several functions who use various properties of User.
With partial protocols you can reuse attributes without having to define
many overlapping protocols.
Inspired by clojure spec.

(exact syntax TBD)

class User(Protocol):
    id: int
    name: str
    is_premium: bool
    address: Address

class Address(Protocol):
    street: str
    city: str
    country: str

from quacks import _

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

def greet(u: User[_.name.address[_.country]]) -> None:
    ...  # access `name` and `address.country` attributes

u: User = ...



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