Python Redis Cache

cache.py

import cPickle
import logging

import redis


TIMEOUT = 60 * 60
_redis = None


def _get_redis():
    """Return a StrictRedis instance. Initialize one first if necessary."""

    global _redis
    if not _redis:
        _redis = redis.StrictRedis()
    return _redis


def set(key, value, timeout=TIMEOUT):
    """Cache the given key-value pair.

    Args:
        key: the cache key.
        value: the value to cache.
        timeout: the expiration timeout for the cache entry in seconds,
                 defaults to 1 minute.
    """

    value = cPickle.dumps(value)
    _get_redis().pipeline().set(key, value).expire(key, timeout).execute()


def get(key):
    """Retrieve the value associated with the given key from the cache.

    Args:
        the cache key to fetch.

    Returns:
        the cached value or None if it doesn't exist.
    """

    value = _get_redis().get(key)
    value = (value and cPickle.loads(value)) or None

    if value is not None:
        logging.debug('Cache hit for %s' % key)

    return value


def flush(pattern='', batch=1000):
    """Flush the cache by evicting all entries or only entries whose keys
    match a given pattern.

    Args:
        pattern: evict only the keys that match this pattern.
        batch: delete the keys in groups of this size.
    """

    red = _get_redis()
    keys = red.keys('%s*' % pattern)

    [red.delete(*keys[i:i + batch]) for i in xrange(0, len(keys), batch)]