Fixed #583 -- Added app_directories template loader, which searches for templates in 'templates' directory in each INSTALLED_APPS package. It's turned off by default.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@892 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/core/template/loaders/app_directories.py

@@ -0,0 +1,28 @@
+# Wrapper for loading templates from "template" directories in installed app packages.
+
+from django.conf.settings import INSTALLED_APPS, TEMPLATE_FILE_EXTENSION
+from django.core.template import TemplateDoesNotExist
+import os
+
+# At compile time, cache the directories to search.
+app_template_dirs = []
+for app in INSTALLED_APPS:
+    i = app.rfind('.')
+    m, a = app[:i], app[i+1:]
+    mod = getattr(__import__(m, '', '', [a]), a)
+    template_dir = os.path.join(os.path.dirname(mod.__file__), 'templates')
+    if os.path.isdir(template_dir):
+        app_template_dirs.append(template_dir)
+
+# It won't change, so convert it to a tuple to save memory.
+app_template_dirs = tuple(app_template_dirs)
+
+def load_template_source(template_name, template_dirs=None):
+    for template_dir in app_template_dirs:
+        filepath = os.path.join(template_dir, template_name) + TEMPLATE_FILE_EXTENSION
+        try:
+            return open(filepath).read()
+        except IOError:
+            pass
+    raise TemplateDoesNotExist, template_name
+load_template_source.is_usable = True