Index: Tkinter.py
===================================================================
--- Tkinter.py	(revision 67239)
+++ Tkinter.py	(revision 67259)
@@ -132,12 +132,25 @@
     Call this function to inhibit that the first instance of
     Tk is used for windows without an explicit parent window.
     """
-    global _support_default_root
+    global _support_default_root, _default_root
     _support_default_root = 0
-    global _default_root
     _default_root = None
     del _default_root
 
+def setup_master(master=None):
+    """If master is not None, itself is returned. Otherwise attempt
+    getting a new master or the default one and return it.
+
+    If it is not allowed to use the default root and master is None,
+    RuntimeError is raised."""
+    if master is None:
+        if _support_default_root:
+            master = _default_root or Tk()
+        else:
+            raise RuntimeError("No master specified and Tkinter is "
+                "configured to not support default root")
+    return master
+
 def _tkerror(err):
     """Internal function."""
     pass