Oops, this file was apparently never added to the repository. Now it is.
diff --git a/Tools/idle/config-mac.txt b/Tools/idle/config-mac.txt
new file mode 100644
index 0000000..ee36e13
--- /dev/null
+++ b/Tools/idle/config-mac.txt
@@ -0,0 +1,3 @@
+[EditorWindow]
+font-name= monaco
+font-size= 9