Fixed #18770 -- memcached cache backend expects byte strings as keys

from django.core.cache.backends.base import BaseCache, InvalidCacheBackendError

from django.utils import six

from django.utils.encoding import smart_str

class BaseMemcachedCache(BaseCache):

    def __init__(self, server, params, library, value_not_found_exception):

            timeout += int(time.time())

        return int(timeout)

    def make_key(self, key, version=None):

        # Python 2 memcache requires the key to be a byte string.

        return smart_str(super(BaseMemcachedCache, self).make_key(key, version))

    def add(self, key, value, timeout=0, version=None):

        key = self.make_key(key, version=version)

        return self._cache.add(key, value, self._get_memcache_timeout(timeout))