issue 4804: Provide checks for the format string of strftime, and for the "mode" string of fopen on Windows. These strings are user provided from python and so we can avoid invoking the C runtime invalid parameter handler by first checking that they are valid.

Lib/test/test_file.py

@@ -154,7 +154,7 @@ class OtherFileTests(unittest.TestCase):
         for name in (TESTFN, unicode(TESTFN), unicode(TESTFN + '\t')):
             try:
                 f = open(name, "rr")
-            except IOError:
+            except (IOError, ValueError):
                 pass
             else:
                 f.close()