the default class attr is needed!
diff --git a/Lib/idlelib/IOBinding.py b/Lib/idlelib/IOBinding.py
index 5a15995..6ab4db0 100644
--- a/Lib/idlelib/IOBinding.py
+++ b/Lib/idlelib/IOBinding.py
@@ -242,6 +242,7 @@
 
     eol = r"(\r\n)|\n|\r"  # \r\n (Windows), \n (UNIX), or \r (Mac)
     eol_re = re.compile(eol)
+    eol_convention = os.linesep  # default
 
     def loadfile(self, filename):
         try: