cache.py

import aioredis
import asyncio
import json

from django.conf import settings


class Backend:
    class NotFound(Exception):
        pass

    async def get(self, key):
        raise NotImplementedError

    async def set(self, key):
        raise NotImplementedError


class Dummy(Backend):
    def __init__(self):
        self._cache = {}

    async def get(self, key):
        try:
            return self._cache[key]
        except KeyError:
            raise self.NotFound(key)

    async def set(self, key, value):
        self._cache[key] = value


class Redis(Backend):
    def __init__(self, params):
        self.params = params
        self._redis = None

    async def redis(self):
        if self._redis:
            return self._redis
        self._redis = await aioredis.create_redis(
            loop=asyncio.get_event_loop(), **self.params
        )
        return self._redis

    async def get(self, key):
        r = await self.redis()
        try:
            v = await r.get(key)
        except KeyError:
            raise self.NotFound(key)
        try:
            return json.loads(v)
        except TypeError:
            # Null, empty string, etc.
            return v

    async def set(self, key, value):
        r = await self.redis()
        await r.set(key, json.dumps(value))


def get_default():
    return Redis(settings.ASYNC_REDIS_PARAMS)