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from __future__ import unicode_literals
from django.core.cache import InvalidCacheBackendError, caches
from django.core.cache.utils import make_template_fragment_key
from django.template import (
Library, Node, TemplateSyntaxError, VariableDoesNotExist,
)
register = Library()
class CacheNode(Node):
def __init__(self, nodelist, expire_time_var, fragment_name, vary_on, cache_name):
self.nodelist = nodelist
self.expire_time_var = expire_time_var
self.fragment_name = fragment_name
self.vary_on = vary_on
self.cache_name = cache_name
def render(self, context):
try:
expire_time = self.expire_time_var.resolve(context)
except VariableDoesNotExist:
raise TemplateSyntaxError('"cache" tag got an unknown variable: %r' % self.expire_time_var.var)
try:
expire_time = int(expire_time)
except (ValueError, TypeError):
raise TemplateSyntaxError('"cache" tag got a non-integer timeout value: %r' % expire_time)
if self.cache_name:
try:
cache_name = self.cache_name.resolve(context)
except VariableDoesNotExist:
raise TemplateSyntaxError('"cache" tag got an unknown variable: %r' % self.cache_name.var)
try:
fragment_cache = caches[cache_name]
except InvalidCacheBackendError:
raise TemplateSyntaxError('Invalid cache name specified for cache tag: %r' % cache_name)
else:
try:
fragment_cache = caches['template_fragments']
except InvalidCacheBackendError:
fragment_cache = caches['default']
vary_on = [var.resolve(context) for var in self.vary_on]
cache_key = make_template_fragment_key(self.fragment_name, vary_on)
value = fragment_cache.get(cache_key)
if value is None:
value = self.nodelist.render(context)
fragment_cache.set(cache_key, value, expire_time)
return value
@register.tag('cache')
def do_cache(parser, token):
"""
This will cache the contents of a template fragment for a given amount
of time.
Usage::
{% load cache %}
{% cache [expire_time] [fragment_name] %}
.. some expensive processing ..
{% endcache %}
This tag also supports varying by a list of arguments::
{% load cache %}
{% cache [expire_time] [fragment_name] [var1] [var2] .. %}
.. some expensive processing ..
{% endcache %}
Optionally the cache to use may be specified thus::
{% cache .... using="cachename" %}
Each unique set of arguments will result in a unique cache entry.
"""
nodelist = parser.parse(('endcache',))
parser.delete_first_token()
tokens = token.split_contents()
if len(tokens) < 3:
raise TemplateSyntaxError("'%r' tag requires at least 2 arguments." % tokens[0])
if len(tokens) > 3 and tokens[-1].startswith('using='):
cache_name = parser.compile_filter(tokens[-1][len('using='):])
tokens = tokens[:-1]
else:
cache_name = None
return CacheNode(nodelist,
parser.compile_filter(tokens[1]),
tokens[2], # fragment_name can't be a variable.
[parser.compile_filter(t) for t in tokens[3:]],
cache_name,
)
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