At Tim Peters' recommendation, add a dummy flush() method to PseudoFile.
diff --git a/Tools/idle/PyShell.py b/Tools/idle/PyShell.py
index e197ad6..8bee5d5 100644
--- a/Tools/idle/PyShell.py
+++ b/Tools/idle/PyShell.py
@@ -593,6 +593,9 @@
     def writelines(self, l):
         map(self.write, l)
 
+    def flush(self):
+        pass
+
 
 def main():
     debug = 0