diff -r d7ae8a84f443 Lib/idlelib/PyShell.py
--- a/Lib/idlelib/PyShell.py	Wed Jun 26 15:11:12 2013 -0400
+++ b/Lib/idlelib/PyShell.py	Wed Jun 26 20:52:19 2013 -0400
@@ -45,35 +45,32 @@
 # internal warnings to the console.  ScriptBinding.check_syntax() will
 # temporarily redirect the stream to the shell window to display warnings when
 # checking user's code.
-global warning_stream
-warning_stream = sys.__stderr__
-try:
-    import warnings
-except ImportError:
-    pass
-else:
-    def idle_showwarning(message, category, filename, lineno,
-                         file=None, line=None):
-        if file is None:
-            file = warning_stream
-        try:
-            file.write(warnings.formatwarning(message, category, filename,
-                                              lineno, line=line))
-        except OSError:
-            pass  ## file (probably __stderr__) is invalid, warning dropped.
-    warnings.showwarning = idle_showwarning
-    def idle_formatwarning(message, category, filename, lineno, line=None):
-        """Format warnings the IDLE way"""
-        s = "\nWarning (from warnings module):\n"
-        s += '  File \"%s\", line %s\n' % (filename, lineno)
-        if line is None:
-            line = linecache.getline(filename, lineno)
-        line = line.strip()
-        if line:
-            s += "    %s\n" % line
-        s += "%s: %s\n>>> " % (category.__name__, message)
-        return s
-    warnings.formatwarning = idle_formatwarning
+
+warning_stream = sys.__stderr__  # None, at least on Windows, if no console.
+import warnings
+
+def idle_formatwarning(message, category, filename, lineno, line=None):
+    """Format warnings the IDLE way"""
+    s = "\nWarning (from warnings module):\n"
+    s += '  File \"%s\", line %s\n' % (filename, lineno)
+    if line is None:
+        line = linecache.getline(filename, lineno)
+    line = line.strip()
+    if line:
+        s += "    %s\n" % line
+    s += "%s: %s\n>>> " % (category.__name__, message)
+    return s
+
+def idle_showwarning(
+        message, category, filename, lineno, file=None, line=None):
+    """Replacement for warnings.showwarnings, in main()"""
+    if file is None:
+        file = warning_stream
+    try:
+        file.write(idle_formatwarning(
+                message, category, filename, lineno, line=line))
+    except AttributeError, OSError:
+        pass  # if file (probably __stderr__) is invalid, skip warning.
 
 def extended_linecache_checkcache(filename=None,
                                   orig_checkcache=linecache.checkcache):
@@ -1421,6 +1418,7 @@
 def main():
     global flist, root, use_subprocess
 
+    warnings.showwarning = idle_showwarning
     use_subprocess = True
     enable_shell = False
     enable_edit = False
diff -r d7ae8a84f443 Lib/idlelib/run.py
--- a/Lib/idlelib/run.py	Wed Jun 26 15:11:12 2013 -0400
+++ b/Lib/idlelib/run.py	Wed Jun 26 20:52:19 2013 -0400
@@ -23,29 +23,33 @@
 
 LOCALHOST = '127.0.0.1'
 
-try:
-    import warnings
-except ImportError:
-    pass
-else:
-    def idle_formatwarning_subproc(message, category, filename, lineno,
-                                   line=None):
-        """Format warnings the IDLE way"""
-        s = "\nWarning (from warnings module):\n"
-        s += '  File \"%s\", line %s\n' % (filename, lineno)
-        if line is None:
-            line = linecache.getline(filename, lineno)
-        line = line.strip()
-        if line:
-            s += "    %s\n" % line
-        s += "%s: %s\n" % (category.__name__, message)
-        return s
-    warnings.formatwarning = idle_formatwarning_subproc
+import warnings
 
+def idle_formatwarning_subproc(message, category, filename, lineno, line=None):
+    """Format warnings the IDLE way for the user subprocess"""
+    s = "\nWarning (from warnings module):\n"
+    s += '  File \"%s\", line %s\n' % (filename, lineno)
+    if line is None:
+        line = linecache.getline(filename, lineno)
+    line = line.strip()
+    if line:
+        s += "    %s\n" % line
+    s += "%s: %s\n" % (category.__name__, message)
+    return s
+
+def idle_showwarning_subproc(
+        message, category, filename, lineno, file=None, line=None):
+    """Replaces warnings.showwarning in main."""
+    if file is None:
+        file = sys.stderr
+    try:
+        file.write(idle_formatwarning_subproc(
+                message, category, filename, lineno, line))
+    except IOError:
+        pass # the file (probably stderr) is invalid - this warning gets lost.
 
 tcl = tkinter.Tcl()
 
-
 def handle_tk_events(tcl=tcl):
     """Process any tk events that are ready to be dispatched if tkinter
     has been imported, a tcl interpreter has been created and tk has been
@@ -91,6 +95,9 @@
         print("IDLE Subprocess: no IP port passed in sys.argv.",
               file=sys.__stderr__)
         return
+    
+    warnings.showwarning = idle_showwarning_subproc
+ 
     sys.argv[:] = [""]
     sockthread = threading.Thread(target=manage_socket,
                                   name='SockThread',