A memcached helper class.

This little class wraps the memcache functionality:

• It allows objects to expire after a default or custom age.
• It allows lazy evaluation of default values (think dict.setdefault, with real lazy behavior) by hiding the default value behind a lambda.

import memcache
import time


class Cache(object):
    def __init__(self, cache_addresses, default_timeout=30*60): 
        self.default_timeout = default_timeout
        self.cache = memcache.Client(cache_addresses)

    def get(self, key, default=lambda:None, timeout=None):
        obj_timestamp = self.cache.get(key)
        if obj_timestamp is None:
            obj = default()
            self.set(key, obj)
        else:
            obj,timestamp = obj_timestamp
            if timeout is None: timeout = self.default_timeout
            if time.time() - timestamp > timeout:
                self.cache.delete(key)
                obj = default()
                self.set(key, obj)
        return obj

    def set(self, key, obj):
        self.cache.set(key, (obj, time.time()))
         
>>> tc = Cache(['127.0.0.1:1979'])
>>> results = tc.get('some_big_list', lambda:build_some_big_list())

An advantage of using this class, is that if the memcached process dies, your process will continue to work as normal, as long as a default is provided to the .get method call.