Use a key function that is safe for use w/ memcache

lib/util/memcache.py

@@ -0,0 +1,18 @@
+"""
+This module provides a KEY_FUNCTION suitable for use with a memcache backend
+so that we can cache any keys, not just ones that memcache would ordinarily accept
+"""
+from django.utils.hashcompat import md5_constructor
+from django.utils.encoding import smart_str
+import string
+
+def safe_key(key, key_prefix, version):
+    safe_key = smart_str(key)
+    for char in safe_key:
+        if ord(char) < 33 or ord(char) == 127:
+            safe_key = safe_key.replace(char, '_')
+
+    if len(safe_key) > 250:
+        safe_key = md5_constructor(safe_key)
+
+    return ":".join([key_prefix, str(version), safe_key])