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Refs #30181 -- Corrected note about storing None in the cache.

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Nick Pope 2020-12-17 07:26:30 +01:00 committed by Mariusz Felisiak
parent 8f384505ee
commit d23dad5778
1 changed files with 15 additions and 3 deletions
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18
docs/topics/cache.txt
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@ -839,9 +839,21 @@ 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::