Issue #4237: io.FileIO() was raising invalid warnings caused by insufficient...

Issue #4237: io.FileIO() was raising invalid warnings caused by insufficient initialization of PyFileIOObject struct members.

Lib/test/test_io.py

@@ -1236,6 +1236,13 @@ class MiscIOTest(unittest.TestCase):
             else:
                 self.assert_(issubclass(obj, io.IOBase))
 
+    def test_fileio_warnings(self):
+        with test_support.check_warnings() as w:
+            self.assertEqual(w.warnings, [])
+            self.assertRaises(TypeError, io.FileIO, [])
+            self.assertEqual(w.warnings, [])
+            self.assertRaises(ValueError, io.FileIO, "/some/invalid/name", "rt")
+            self.assertEqual(w.warnings, [])
 
 def test_main():
     test_support.run_unittest(IOTest, BytesIOTest, StringIOTest,

Modules/_fileio.c

@@ -86,6 +86,10 @@ fileio_new(PyTypeObject *type, PyObject *args, PyObject *kews)
 	self = (PyFileIOObject *) type->tp_alloc(type, 0);
 	if (self != NULL) {
 		self->fd = -1;
+		self->readable = 0;
+		self->writable = 0;
+		self->seekable = -1;
+		self->closefd = 1;
 		self->weakreflist = NULL;
 	}
 
@@ -179,8 +183,6 @@ fileio_init(PyObject *oself, PyObject *args, PyObject *kwds)
 	    }
 	}
 
-	self->readable = self->writable = 0;
-	self->seekable = -1;
 	s = mode;
 	while (*s) {
 		switch (*s++) {