Fix closes issue12438  - idlelib.PyShell's showformatwarning method was passing an incorrect arg.
diff --git a/Lib/idlelib/PyShell.py b/Lib/idlelib/PyShell.py
index 0c95df4..9dd43cf 100644
--- a/Lib/idlelib/PyShell.py
+++ b/Lib/idlelib/PyShell.py
@@ -61,7 +61,7 @@
             file = warning_stream
         try:
             file.write(warnings.formatwarning(message, category, filename,
-                                              lineno, file=file, line=line))
+                                              lineno, line=line))
         except IOError:
             pass  ## file (probably __stderr__) is invalid, warning dropped.
     warnings.showwarning = idle_showwarning