Memoize common lookups during request

Prevents repeated memcached lookups on functions whose values should
remain static for the lifetime of a request.

EDUCATOR-1731

openedx/core/djangoapps/theming/helpers.py

@@ -19,14 +19,17 @@ from openedx.core.djangoapps.theming.helpers_dirs import (
     get_theme_dirs,
     get_themes_unchecked
 )
-from request_cache.middleware import RequestCache
+from request_cache.middleware import RequestCache, request_cached
 
 logger = getLogger(__name__)  # pylint: disable=invalid-name
 
 
+@request_cached
 def get_template_path(relative_path, **kwargs):
     """
     This is a proxy function to hide microsite_configuration behind comprehensive theming.
+
+    The calculated value is cached for the lifetime of the current request.
     """
     # We need to give priority to theming over microsites
     # So, we apply microsite override only if there is no associated site theme

openedx/core/djangoapps/theming/tests/test_helpers.py

@@ -12,6 +12,7 @@ from openedx.core.djangoapps.theming import helpers as theming_helpers
 from openedx.core.djangoapps.theming.helpers import get_template_path_with_theme, strip_site_theme_templates_path, \
     get_themes, Theme, get_theme_base_dir
 from openedx.core.djangolib.testing.utils import skip_unless_cms, skip_unless_lms
+from request_cache.middleware import RequestCache
 
 
 class TestHelpers(TestCase):
@@ -189,6 +190,8 @@ class TestHelpers(TestCase):
                     mock_microsite_backend.get_template = Mock(return_value="/microsite/about.html")
                     self.assertEqual(theming_helpers.get_template_path("about.html"), "about.html")
 
+        RequestCache.clear_request_cache()
+
         # if the current site does not have associated SiteTheme then get_template_path should return microsite override
         with patch(
             "openedx.core.djangoapps.theming.helpers.current_request_has_associated_site_theme",