Memcached Compare-And-Set pattern yields wrong result - django

Question

I'm trying to implement memcached compare-and-set pattern, following the instructions of Guido at:
http://neopythonic.blogspot.nl/2011/08/compare-and-set-in-memcache.html
However, I don't seem to get it right and I have no idea what's wrong. The files below use Django (1.4.5 Final) and python-memcache (1.48).
settings.py
CACHES = {
'default': {
'BACKEND': 'django.core.cache.backends.memcached.MemcachedCache',
'LOCATION': '127.0.0.1:11211',
}
}
djangocache.py
#!/usr/bin/env python
from django.core.cache import cache
import multiprocessing.dummy
django_key = "TEST"
cached_key = cache.make_key(django_key).encode("UTF-8")
def add_to_cache(item):
client = cache._cache
#client = cache._lib.Client(cache._servers)
while True:
items = client.gets(cached_key)
if client.cas(cached_key, items+(item,)):
break
if __name__ == "__main__":
cache.set(django_key, ())
p = multiprocessing.dummy.Pool(2)
p.map(add_to_cache, range(10))
print(len(cache.get(django_key)))
Running it:
mzialla#Q330 ~/test $ DJANGO_SETTINGS_MODULE=settings python djangocache.py
5
It occasionally outputs 6, 7, etc. like you would expect when dealing with race conditions. I've tried multiple client instantiations (see comment).
Help?

Answer 1

python-memcached disables cas by default. Enable it by adding
client.cache_cas = True
to your code.
Credits to Nate Thelen, who's comment I discovered right after asking this question.