JSON decoder in Python

example.py

from main import *


@dataclass
class Measurment:
    temp: float
    humidity: float
    # date: datetime


@dataclass
class Sensor:
    name: str
    location: str
    uptime: float
    # charging: bool
    readings: List[Measurment]


data = {
    "name": "sigma sensor",
    "location": "district 9",
    "uptime": "39",
    "charging": "yes",
    "readings": [
        {"temp": "20", "humidity": "0.4", "date": "2022/06/12"},
        {"temp": "25", "humidity": "0.45", "date": "July 03 2021"},
        {"temp": "30", "humidity": "0.39", "date": "2020-05-03"},
    ],
}


dec_m = decoders_to(Measurment, key("temp"), key("humidity"))
dec_s = decoders_to(
    Sensor,
    key("name"),
    key("location"),
    key("uptime") >> float_,
    key("readings") >> dec_m.list(),
)
print(dec_s(data))

main.py

from dataclasses import dataclass                                                                                                                                                                                                                     [8/618]

from typing import Any, Callable, Dict, Generic, List, Iterable, Tuple, TypeVar


A = TypeVar("A")
B = TypeVar("B")


@dataclass
class Decoder(Generic[A]):
    decode: Callable[[Dict], A]

    def __call__(self, data: Dict) -> A:
        return self.decode(data)

    def fmap(self, f: Callable[[A], B]) -> "Decoder[B]":
        return Decoder(lambda data: f(self(data)))

    def __rshift__(self: "Decoder[Dict]", other: "Decoder[B]"):
        """Sequence two decoders. The first decoder should return a dictionary."""
        return Decoder(lambda data: other(self(data)))

    def __pow__(self, other: "Decoder[B]") -> "Decoder[Tuple[A, B]]":
        """Combine two decoders."""
        return combine2(self, other)

    def to(self, cls: object) -> "Decoder[Any]":
        return self.fmap(lambda args: cls(*args))

    def list(self):
        return Decoder(lambda data: [self(datum) for datum in data])


def lift(a) -> Decoder:
    return Decoder(lambda _: a)


identity: Decoder[Any] = Decoder(lambda data: data)


def combine2(d1: Decoder[A], d2: Decoder[B]) -> Decoder[Tuple[A, B]]:
    return Decoder(lambda data: (d1(data), d2(data)))


def combinen(decoders: Iterable[Decoder]) -> Decoder[Tuple]:
    return Decoder(lambda data: tuple(d(data) for d in decoders))


def decoders_to(cls, *decoders) -> Decoder:
    return combinen(decoders).to(cls)


def key(k: str) -> Decoder[Dict]:
    return Decoder(lambda data: data[k])


def index(i: int) -> Decoder[Dict]:
    return Decoder(lambda data: data[i])


float_: Decoder[float] = Decoder(lambda data: float(data))