diff options
Diffstat (limited to 'docs/topics/cache.txt')
| -rw-r--r-- | docs/topics/cache.txt | 18 |
1 files changed, 15 insertions, 3 deletions
diff --git a/docs/topics/cache.txt b/docs/topics/cache.txt index f8e9f34380..cb5d21e7b0 100644 --- a/docs/topics/cache.txt +++ b/docs/topics/cache.txt @@ -824,9 +824,21 @@ If the object doesn't exist in the cache, ``cache.get()`` returns ``None``:: >>> cache.get('my_key') None -We advise against storing the literal value ``None`` in the cache, because you -won't be able to distinguish between your stored ``None`` value and a cache -miss signified by a return value of ``None``. +If you need to determine whether the object exists in the cache and you have +stored a literal value ``None``, use a sentinel object as the default:: + + >>> sentinel = object() + >>> cache.get('my_key', sentinel) is sentinel + False + >>> # Wait 30 seconds for 'my_key' to expire... + >>> cache.get('my_key', sentinel) is sentinel + True + +.. admonition:: ``MemcachedCache`` + + Due to a ``python-memcached`` limitation, it's not possible to distinguish + between stored ``None`` value and a cache miss signified by a return value + of ``None`` on the deprecated ``MemcachedCache`` backend. ``cache.get()`` can take a ``default`` argument. This specifies which value to return if the object doesn't exist in the cache:: |