Load templates at descriptor load

* instead of being lazy

common/lib/xmodule/xmodule/template_module.py

@@ -2,7 +2,6 @@ from xmodule.x_module import XModule
 from xmodule.raw_module import RawDescriptor
 from lxml import etree
 from mako.template import Template
-from xmodule.util.decorators import lazyproperty
 
 
 class CustomTagModule(XModule):
@@ -31,33 +30,37 @@ class CustomTagModule(XModule):
                  instance_state=None, shared_state=None, **kwargs):
         XModule.__init__(self, system, location, definition, descriptor,
                          instance_state, shared_state, **kwargs)
+        self.html = definition['html']
 
-        xmltree = etree.fromstring(self.definition['data'])
+    def get_html(self):
+        return self.html
+
+
+class CustomTagDescriptor(RawDescriptor):
+    """ Descriptor for custom tags.  Loads the template when created."""
+    module_class = CustomTagModule
+
+    @classmethod
+    def definition_from_xml(cls, xml_object, system):
+        definition = RawDescriptor.definition_from_xml(xml_object, system)
+
+        # Render the template and save it.
+        xmltree = etree.fromstring(definition['data'])
         if 'impl' in xmltree.attrib:
-            self._template_name = xmltree.attrib['impl']
+            template_name = xmltree.attrib['impl']
         else:
             # VS[compat]  backwards compatibility with old nested customtag structure
             child_impl = xmltree.find('impl')
             if child_impl is not None:
-                self._template_name = child_impl.text
+                template_name = child_impl.text
             else:
                 # TODO (vshnayder): better exception type
                 raise Exception("Could not find impl attribute in customtag {0}"
                                 .format(location))
-        
-        self._params = dict(xmltree.items())
 
+        params = dict(xmltree.items())
+        with system.resources_fs.open('custom_tags/{name}'
+                                   .format(name=template_name)) as template:
+            definition['html'] = Template(template.read()).render(**params)
 
-    @lazyproperty
-    def html(self):
-        with self.system.filestore.open(
-                'custom_tags/{name}'.format(name=self._template_name)) as template:
-            return Template(template.read()).render(**self._params)
-        
-
-    def get_html(self):
-        return self.html
-
-
-class CustomTagDescriptor(RawDescriptor):
-    module_class = CustomTagModule
+        return definition