Fix SF buf #476953: Bad more for opening file gives bad msg.

If fopen() fails with EINVAL it means that the mode argument is
invalid.  Return the mode in the error message instead of the
filename.

Lib/test/test_file.py

@@ -46,4 +46,15 @@ else:
     print "writelines accepted sequence of non-string objects"
 f.close()
 
+# verify that we get a sensible error message for bad made argument
+bad_mode = "qwerty"
+try:
+    open(TESTFN, bad_mode)
+except IOError, msg:
+    s = str(msg)
+    if s.find(TESTFN) != -1 or s.find(bad_mode) == -1:
+        print "bad error message for invalid mode: %s" % s
+else:
+    print "no error for invalid mode: %s" % bad_mode
+
 os.unlink(TESTFN)

Objects/fileobject.c

@@ -121,13 +121,17 @@ open_the_file(PyFileObject *f, char *name, char *mode)
 	if (f->f_fp == NULL) {
 #ifdef NO_FOPEN_ERRNO
 		/* Metroworks only, not testable, so unchanged */
-		if ( errno == 0 ) {
+		if (errno == 0) {
 			PyErr_SetString(PyExc_IOError, "Cannot open file");
 			Py_DECREF(f);
 			return NULL;
 		}
 #endif
-		PyErr_SetFromErrnoWithFilename(PyExc_IOError, name);
+		if (errno == EINVAL)
+			PyErr_Format(PyExc_IOError, "invalid argument: %s",
+				     mode);
+		else
+			PyErr_SetFromErrnoWithFilename(PyExc_IOError, name);
 		f = NULL;
 	}
 	return (PyObject *)f;