memcache extension for Jinja2 on Google AppEngine

gistfile1.py

from google.appengine.api import memcache

from jinja2 import nodes
from jinja2.ext import Extension, next

"""

A great Jinja2 Extension for quicker caching of fully rendered content using
Memcache on AppEngine.

Activate this Extension by adding it to the list of Extension on your
Jinja2-Environment-Setup and you'll have a powerful jinja2-macro on
your hand. Then simply wrap the code you want to cached into

{% memcached "my_key" %}
    ... your template code here
{% endmemcached %}

and from the next time the page is rendered this features uses memcache to
cache and retrieve complete rendered parts of the webpage. You'll see an
immediate increase in response time from the second request.

You can do everything within the block - even include other templates.
When the Extension can't find the corresponding result in the memcache it
executes the code normally and saves the resulting string. 

Note: If the given cache-key converts into a faulty value, the code is
executed always and the code never cached. This gives the user the ability
to force execution as the key can be an expression as usually:

{% memcached myModel.cache_key %}
    ... your template code here
{% endmemcached %}

Here for some models (those having a cache_key) caching is allowed, for
others (those where cache_key is False) it is prohibited and the code is
always executed.

*Note*: the key is never de-validated or deleted. Cache-validation
responsibility must be taken by the developer somewhere else. However you
can specify the max-timeout passed to the memcache-call by passing a number
as the second value when calling memcached:

{% memcached myModel.cache_key 3600 %}
    ... your template code here
{% endmemcached %}


================
 2012 © by Benjamin Kampmann < ben . kampmann at gmail . com >

 Latest version always available as a gist: https://gist.github.com/2352035


"""


class MemcachedExtension(Extension):
    tags = set(["memcached"]) 

    def parse(self, parser):
        lineno = parser.stream.next().lineno
        args = [parser.parse_expression(), 
                parser.stream.current.type != 'block_end' and 
                    parser.parse_expression() or nodes.Const(None)]

        body = parser.parse_statements(['name:endmemcached'], drop_needle=True)
        return nodes.CallBlock(
            self.call_method('_cache', args), [], [], body
        ).set_lineno(lineno)

    def _cache(self, keyname, timeout, caller):
        if not keyname:
            return caller()

        value = memcache.get(keyname)
        if not value:
            value = caller()
            memcache.set(keyname, value, time=timeout or 0)
        
        return value


memcached = MemcachedExtension