'loads the value specified from the disk and stores it in the in-memory
cache
:param key:
the key to load from disk; if None, all entries in the cache
will be read from disk'

def load(self, key=None):

    with self._write_lock:
        if (key is None):
            for entry in os.listdir(self.cache_path):
                if os.path.isfile(entry):
                    entry_name = os.path.basename[entry]
                    try:
                        self._objects[entry_name] = self._read(entry_name)
                    except:
                        print u'error    while    loading    {0}'.format(entry_name)
        else:
            self._objects[key] = self._read(key)
    if (key is not None):
        return self._objects[key]
