diff --git a/rhodecode/lib/memory_lru_dict.py b/rhodecode/lib/memory_lru_dict.py
--- a/rhodecode/lib/memory_lru_dict.py
+++ b/rhodecode/lib/memory_lru_dict.py
@@ -54,7 +54,7 @@ class LRUDict(LRUCache):
         del self.data[key]
 
     def keys(self):
-        return self.data.keys()
+        return list(self.data.keys())
 
 
 class LRUDictDebug(LRUDict):
@@ -62,12 +62,13 @@ class LRUDictDebug(LRUDict):
     Wrapper to provide some debug options
     """
     def _report_keys(self):
-        elems_cnt = '%s/%s' % (len(self.keys()), self.size)
+
         # trick for pformat print it more nicely
         fmt = '\n'
         for cnt, elem in enumerate(self.keys()):
-            fmt += '%s - %s\n' % (cnt+1, safe_str(elem))
-        log.debug('current LRU keys (%s):%s', elems_cnt, fmt)
+            fmt += f'{cnt+1} - {safe_str(elem)}\n'
+
+        log.debug('current LRU keys (%s/%s):%s', len(self.keys()), self.size, fmt)
 
     def __getitem__(self, key):
         self._report_keys()