diff --git a/docs/topics/cache.txt b/docs/topics/cache.txt
index 6827b3f40e..33e0f72e95 100644
--- a/docs/topics/cache.txt
+++ b/docs/topics/cache.txt
@@ -1038,7 +1038,7 @@ key version to provide a final cache key. By default, the three parts
 are joined using colons to produce a final string::
 
     def make_key(key, key_prefix, version):
-        return ':'.join([key_prefix, str(version), key])
+        return '%s:%s:%s' % (key_prefix, version, key)
 
 If you want to combine the parts in different ways, or apply other
 processing to the final key (e.g., taking a hash digest of the key