Simple local cache implementation

gistfile1.py

import os
import sqlite3
import simplejson
import time


class LocalCache(object):

    def __init__(self, path='/run/shm/cache.db'):
        self.db = sqlite3.Connection(path)
        with self.db:
            self.db.execute(
                """create table if not exists cache (
                   key TEXT PRIMARY KEY,
                   value TEXT,
                   expires REAL)""")
            # Since this is in shared memory turn journal off
            self.db.execute("pragma journal_mode = OFF")

    def _sanitize_time(self, time):
        if time > 0:
            return time.time() + time

    def set(self, key, value, serialize=True, time=0, min_compress_len=0):
        time = self._sanitize_time(time)
        value = simplejson.dumps(value)
        with self.db:
            self.db.execute(
                "replace into cache (key, value, expires) values (?, ?, ?)",
                (key, value, time))

    def get(self, key):
        with self.db:
            result = self.db.execute(
                "select value, expires from cache where key = ?",
                (key,)).fetchone()
        if result and result[1] < time.time():
            return simplejson.loads(result[0])
        else:
            return None

    def incr(self, key, delta=1, time=0):
        # TODO: there is a race condition here, but this is the 
        # closest I can get at the moment
        time = self._sanitize_time(time)
        with self.db:
            self.db.execute(
                "insert or ignore into cache (key, value, expires) values (?, ?, ?)",
                (key, '0', time))
            self.db.execute(
                "update cache set value=value + ? where key = ?",
                (delta, key))
        return self.get(key)

    def decr(self, key, delta=1, time=0):
        return self.incr(key, -delta, time)

    def delete(self, key):
        with self.db:
            self.db.execute(
                "delete from cache where key = ?",
                key)

    def set_multi(self, mapping, server_key=None, serialize=True, time=0,
                  min_compress_len=0):
        raise NotImplementedError()

    def get_multi(self, keys, server_key=None):
        raise NotImplementedError()