示例扩展下面的例子用 Werkzeug 的缓存 contrib 模块为 Jinja2 实现了一个 cache 标签: from jinja2 import nodes
from jinja2.ext import Extension
class FragmentCacheExtension(Extension):
# a set of names that trigger the extension.
tags = set(['cache'])
def __init__(self, environment):
super(FragmentCacheExtension, self).__init__(environment)
# add the defaults to the environment
environment.extend(
fragment_cache_prefix='',
fragment_cache=None
)
def parse(self, parser):
# the first token is the token that started the tag. In our case
# we only listen to ``'cache'`` so this will be a name token with
# `cache` as value. We get the line number so that we can give
# that line number to the nodes we create by hand.
lineno = parser.stream.next().lineno
# now we parse a single expression that is used as cache key.
args = [parser.parse_expression()]
# if there is a comma, the user provided a timeout. If not use
# None as second parameter.
if parser.stream.skip_if('comma'):
args.append(parser.parse_expression())
else:
args.append(nodes.Const(None))
# now we parse the body of the cache block up to `endcache` and
# drop the needle (which would always be `endcache` in that case)
body = parser.parse_statements(['name:endcache'], drop_needle=True)
# now return a `CallBlock` node that calls our _cache_support
# helper method on this extension.
return nodes.CallBlock(self.call_method('_cache_support', args),
[], [], body).set_lineno(lineno)
def _cache_support(self, name, timeout, caller):
"""Helper callback."""
key = self.environment.fragment_cache_prefix + name
# try to load the block from the cache
# if there is no fragment in the cache, render it and store
# it in the cache.
rv = self.environment.fragment_cache.get(key)
if rv is not None:
return rv
rv = caller()
self.environment.fragment_cache.add(key, rv, timeout)
return rv
而这是你在环境中使用它的方式: from jinja2 import Environment
from werkzeug.contrib.cache import SimpleCache
env = Environment(extensions=[FragmentCacheExtension])
env.fragment_cache = SimpleCache()
之后，在模板中可以标记块为可缓存的。下面的例子缓存一个边栏 300 秒: {% cache 'sidebar', 300 %}
<div class="sidebar">
...
</div>
{% endcache %}
扩展 API扩展总是继承
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