Can't delete cache for specific entry in Django

Question

I'm trying to purge cache for one specific Entry when it is saved using signals.

I'm using decorators (signals and render_to) from django-annoying

@signals.post_save(sender=Artigo)
def artigo_post_save(instance, **kwargs):

    from django.http import HttpRequest
    from django.utils.cache import get_cache_key
    from django.core.cache import cache

    # cache.delete(instance.get_absolute_url()) # not work

    request = HttpRequest()
    request.method = "GET"
    request.path = '/' + instance.get_absolute_url()

    print 'request path: ', request.path

    key = get_cache_key(request=request, 
                        key_prefix=settings.CACHE_MIDDLEWARE_KEY_PREFIX)

    print "found key" if cache.has_key(key) else "notfound key"

    if cache.has_key(key):
        cache.delete(key)
        cache.set(key, None, 0)

• The problem is that when I save the model, I get output "notfound key", so the cache continues without purge
• request.path are point properly to my entry path.

Some settings:

SESSION_ENGINE = "django.contrib.sessions.backends.cache"
CACHE_MIDDLEWARE_ANONYMOUS_ONLY = True
CACHE_MIDDLEWARE_KEY_PREFIX = 'cache'
CACHE_MIDDLEWARE_SECONDS = 600

CACHES = {
    'default': {
            'LOCATION': '',
            'BACKEND': 'django.core.cache.backends.locmem.LocMemCache'
     },
}

And the view:

@cache_page(60 * 60)
@render_to('artigo.html')
def artigo(request, categoria_slug, extra_slug="", artigo_slug=""):
    ...

Thank you.

EDIT:
I did Ilvar changes and now i'm getting "found key" as return but I still can't delete cache:

    key = _generate_cache_header_key(key_prefix=settings.CACHE_MIDDLEWARE_KEY_PREFIX, request=request)
    key = key.replace(settings.LANGUAGE_CODE, settings.LANGUAGES[0][0])

Conf:

LANGUAGE_CODE = 'pt-BR'

LANGUAGES = (
        ('pt-BR','Portugues'),
)

• I only have the content updated when I restart the Gevent Server.

Answer 1

cache.set(key, None, 0) should be enough, I've been clearing cache keys that way before.

If you are able to, can you try the cache.clear(), to clear it all? Just to see if it works.

Are non of your cache keys deletable? Is the output of this as expected?

cache.set('testkey', 'testvalue', 600)
cache.get('testkey')
cache.delete('testkey')
cache.get('testkey')
cache.set('testkey', 'testvalue2', 600)
cache.set('testkey', 'another value', 600)
cache.get('testkey')

And have you tried with another caching backend? It looks like everything you are doing is correct.

Maybe the error is in the backend, some configuration that wont let it overwrite keys or something weird..