Backport:

Properly fix SF bug #507298 (Gregor Lingl): shellpython2.2 -Qnew smart
indent error

Use // where int division is intended.

Tools/idle/EditorWindow.py

@@ -466,7 +466,7 @@ class EditorWindow:
         top, bot = self.getwindowlines()
         lineno = self.getlineno(mark)
         height = bot - top
-        newtop = max(1, lineno - height/2)
+        newtop = max(1, lineno - height//2)
         text.yview(float(newtop))
 
     def getwindowlines(self):