djangoplicity-keyedcache 1.5.3

keyedcache

About

Djangoplicity-keyedcache provides a simplified, speedy way to manage caching in Django apps.

Example

The most frequent usage:

from keyedcache import cache_set, cache_get, NotCachedError
import keyedcache

# ... create come object
# cache it
cache_set("product", 123, value=product)
cache_set("product", 123, value=product, length=3600)  # different timeout
# ... delete it
# get it
try:
    value = cache_get("product", 123)
except NotCachedError:
    value = None

# the syntax "parameter=var" does exactly the same as the previous:
try:
    value = cache_get(product=123)
....

# optional deleting
keyedcache.cache_delete('some.temporary.secret')

The reference documentation for these functions is their docs strings.

Advanced examples

More rare usage:

# it is better sometimes to call the internal function `cache_key` to
# combine complicated parameters to one key used multiple times.
cachekey = keyedcache.cache_key('SHIP_company', \
        weight=str(weight), country=country.code, zipcode=zipcode)
try:
    value = cache_get(cachekey)
except NotCachedError:
    value = None
if value == None:
    value = ...long running function...
    cache_set(cachekey, value=value)
    log.info('message %s', cachekey)

...

# Mixin - for models.py - simplified caching for some model
class MyNewModel(models.Model, keyedcache.CachedObjectMixin):
    # some Fields...

    # we can easy cache saving of all objects without writing the keys
    def save(self):
        # ... do somehting
        self.cache_delete()
        super(MyNewModel, self).save()
        self.cache_set()
        return self

Cached function

All values of any slow function evaluated in the future can be cached transparently:

import keyedcache
from time import sleep

def nearest_restaurant(gps_x, gps_y):
   sleep(3)   # internet
   return 'Havana Road' if (gps_x -3) ** 2 + (gps_y - 6) ** 2 <= 1 else 'unknown'

cached_restaurant = keyedcache.cache_function(60)(nearest_restaurant)
print cached_restaurant( 2, 6)  # slow
print cached_restaurant(-3, 4)  # slow
print cached_restaurant( 2, 6)  # fast
keyedcache.cache_delete_function(nearest_restaurant)
print cached_restaurant( 2, 6)  # slow

Optimizing to prevent concurrent multiple calculation of the same function value by concurrent processes is the main reason, why keyedcache is more complicated than could be expected.

Additional first-level caching

If you want first to cache the values temporary in the memory during one request before the normal django cache:

from keyedcache import threaded
threaded.start_listening()

This should be safe also with multithreading.

Cache backend alias

The backend used by cache can be selected by settings variable KEYEDCACHE_ALIAS if the project uses more backends. The default is ‘default’.

Web interface

Cache statistics, cached keys and deleting the cache can be accessed by running the dev server in the test_app directory and going to settings http://127.0.0.1:8000/cache/.

(Urls of in keyedcache are usually mapped to “/cache” by the main application.) The web intergace is for debugging purposes and usage with debug server. If the server is running in production with multiple worker processes, the information provided by the web interface is incomplete. The access to the web interface requires “is_staff” permissions.

Requirements

Python 2.5, 2.6 or 2.7; Django 1.4 or 1.5

(optional) If you want to use the threaded first-level cache, you need to install threaded_multihost.

It is recommended to set a ‘KEY_PREFIX’ to any unique string in your settings.py file. For production caches or for sites with different values SITE_ID it is even obligatory. This allows you to avoid collisions when running more than one site with the same backend. An easy solution is CACHES = {‘defalt’: {… ‘KEY_PREFIX’: str(settings.SITE_ID)}}.

Release notes

ver. 1.5.0

• The cache configuration is made compatible with current versions of Django.

It is currently configured by the varible CACHES. The variable CACHE_PREFIX is currently obsoleted CACHES.