Create a cacheback template tag

cacheback/templatetags/__init__.py

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+

cacheback/templatetags/cacheback.py

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+from __future__ import unicode_literals
+
+import time
+
+from django.core.cache.utils import make_template_fragment_key
+from django.template import (
+    Library, Node, TemplateSyntaxError, VariableDoesNotExist)
+
+from cacheback.base import Job
+
+register = Library()
+
+
+class CacheJob(Job):
+    """Class to handle asynchronous loading of all cacheback template tags"""
+
+    def fetch(self, nodelist, context, expire_time, fragment_name, vary_on):
+        """Render the node"""
+        return self.nodelist.render(context)
+
+    def expiry(self, nodelist, context, expire_time, fragment_name, vary_on):
+        """When to expire"""
+        return time.time() + expire_time
+
+    def key(self, nodelist, context, expire_time, fragment_name, vary_on):
+        """Make the cache key"""
+        return make_template_fragment_key(fragment_name, vary_on)
+
+
+class CacheNode(Node):
+    def __init__(self, nodelist, expire_time_var, fragment_name, vary_on):
+        self.nodelist = nodelist
+        self.expire_time_var = expire_time_var
+        self.fragment_name = fragment_name
+        self.vary_on = vary_on
+
+    def render(self, context):
+        try:
+            expire_time = self.expire_time_var.resolve(context)
+        except VariableDoesNotExist:
+            raise TemplateSyntaxError(
+                '"cacheback" tag got an unknown variable: %r' % self.expire_time_var.var)
+        try:
+            expire_time = int(expire_time)
+        except (ValueError, TypeError):
+            raise TemplateSyntaxError(
+                '"cacheback" tag got a non-integer timeout value: %r' % expire_time)
+
+        vary_on = [var.resolve(context) for var in self.vary_on]
+        return CacheJob().get(self.nodelist, context, expire_time, self.fragment_name, vary_on)
+
+
+@register.tag('cacheback')
+def do_cacheback(parser, token):
+    """
+    This will cache the contents of a template fragment for a given amount
+    of time.
+    Usage::
+        {% load cacheback %}
+        {% cacheback [expire_time] [fragment_name] %}
+            .. some expensive processing ..
+        {% endcacheback %}
+    This tag also supports varying by a list of arguments::
+        {% load cacheback %}
+        {% cacheback [expire_time] [fragment_name] [var1] [var2] .. %}
+            .. some expensive processing ..
+        {% endcacheback %}
+    Each unique set of arguments will result in a unique cache entry.
+    """
+    nodelist = parser.parse(('endcacheback',))
+    parser.delete_first_token()
+    tokens = token.split_contents()
+    if len(tokens) < 3:
+        raise TemplateSyntaxError("'%r' tag requires at least 2 arguments." % tokens[0])
+    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:]],
+    )