Fetch the manifest file only once and store the results in a module level variable.

compressor/cache.py

@@ -62,18 +62,29 @@ def get_offline_manifest_filename():
     return os.path.join(output_dir, settings.COMPRESS_OFFLINE_MANIFEST)
 
 
+_offline_manifest = None
+
 def get_offline_manifest():
-    filename = get_offline_manifest_filename()
-    if default_storage.exists(filename):
-        return simplejson.load(default_storage.open(filename))
-    else:
-        return {}
+    global _offline_manifest
+    if _offline_manifest is None:
+        filename = get_offline_manifest_filename()
+        if default_storage.exists(filename):
+            _offline_manifest = simplejson.load(default_storage.open(filename))
+        else:
+            _offline_manifest = {}
+    return _offline_manifest
+
+
+def flush_offline_manifest():
+    global _offline_manifest
+    _offline_manifest = None    
 
 
 def write_offline_manifest(manifest):
     filename = get_offline_manifest_filename()
     default_storage.save(filename,
                          ContentFile(simplejson.dumps(manifest, indent=2)))
+    flush_offline_manifest()
 
 
 def get_templatetag_cachekey(compressor, mode, kind):

compressor/tests/offline.py

@@ -9,6 +9,7 @@ except ImportError:
 from django.template import Template, Context
 from django.test import TestCase
 
+from compressor.cache import flush_offline_manifest
 from compressor.conf import settings
 from compressor.exceptions import OfflineGenerationError
 from compressor.management.commands.compress import Command as CompressCommand
@@ -134,6 +135,7 @@ class OfflineGenerationTestCase(OfflineTestCaseMixin, TestCase):
     expected_hash = "f5e179b8eca4"
 
     def test_rendering_without_compressing_raises_exception(self):
+        flush_offline_manifest()
         self.assertRaises(OfflineGenerationError,
                           self.template.render, Context({}))