When your application runs slow, throw some caches in. Well, at least it’s the easiest way to speed up things. What does a cache do? Say you have a function that takes some time to complete but the results would still be good enough if they were 5 minutes old. So then the idea is that you actually put the result of that calculation into a cache for some time.
Flask itself does not provide caching for you, but Werkzeug, one of the libraries it is based on, has some very basic cache support. It supports multiple cache backends, normally you want to use a memcached server.
11.1. Setting up a Cache¶
You create a cache object once and keep it around, similar to how
Flask objects are created. If you are using the
development server you can create a
SimpleCache object, that one is a simple
cache that keeps the item stored in the memory of the Python interpreter:
from werkzeug.contrib.cache import SimpleCache cache = SimpleCache()
If you want to use memcached, make sure to have one of the memcache modules supported (you get them from PyPI) and a memcached server running somewhere. This is how you connect to such an memcached server then:
from werkzeug.contrib.cache import MemcachedCache cache = MemcachedCache(['127.0.0.1:11211'])
If you are using App Engine, you can connect to the App Engine memcache server easily:
from werkzeug.contrib.cache import GAEMemcachedCache cache = GAEMemcachedCache()
11.2. Using a Cache¶
Now how can one use such a cache? There are two very important
set(). This is how to use them:
To get an item from the cache call
get() with a string as key name.
If something is in the cache, it is returned. Otherwise that function
rv = cache.get('my-item')
To add items to the cache, use the
method instead. The first argument is the key and the second the value
that should be set. Also a timeout can be provided after which the cache
will automatically remove item.
Here a full example how this looks like normally:
def get_my_item(): rv = cache.get('my-item') if rv is None: rv = calculate_value() cache.set('my-item', rv, timeout=5 * 60) return rv