Issue #4604: Some objects of the I/O library could still be used after

having been closed (for instance, a read() call could return some
previously buffered data). Patch by Dmitry Vasiliev.

Lib/test/test_io.py

@@ -1324,6 +1324,45 @@ class MiscIOTest(unittest.TestCase):
         f.close()
         g.close()
 
+    def test_io_after_close(self):
+        for kwargs in [
+                {"mode": "w"},
+                {"mode": "wb"},
+                {"mode": "w", "buffering": 1},
+                {"mode": "w", "buffering": 2},
+                {"mode": "wb", "buffering": 0},
+                {"mode": "r"},
+                {"mode": "rb"},
+                {"mode": "r", "buffering": 1},
+                {"mode": "r", "buffering": 2},
+                {"mode": "rb", "buffering": 0},
+                {"mode": "w+"},
+                {"mode": "w+b"},
+                {"mode": "w+", "buffering": 1},
+                {"mode": "w+", "buffering": 2},
+                {"mode": "w+b", "buffering": 0},
+            ]:
+            f = io.open(support.TESTFN, **kwargs)
+            f.close()
+            self.assertRaises(ValueError, f.flush)
+            self.assertRaises(ValueError, f.fileno)
+            self.assertRaises(ValueError, f.isatty)
+            self.assertRaises(ValueError, f.__iter__)
+            if hasattr(f, "peek"):
+                self.assertRaises(ValueError, f.peek, 1)
+            self.assertRaises(ValueError, f.read)
+            if hasattr(f, "read1"):
+                self.assertRaises(ValueError, f.read1, 1024)
+            if hasattr(f, "readinto"):
+                self.assertRaises(ValueError, f.readinto, bytearray(1024))
+            self.assertRaises(ValueError, f.readline)
+            self.assertRaises(ValueError, f.readlines)
+            self.assertRaises(ValueError, f.seek, 0)
+            self.assertRaises(ValueError, f.tell)
+            self.assertRaises(ValueError, f.truncate)
+            self.assertRaises(ValueError, f.write, "")
+            self.assertRaises(ValueError, f.writelines, [])
+
 
 def test_main():
     support.run_unittest(IOTest, BytesIOTest, StringIOTest,

Misc/NEWS

@@ -12,6 +12,10 @@ What's New in Python 3.1 alpha 0
 Core and Builtins
 -----------------
 
+- Issue #4604: Some objects of the I/O library could still be used after 
+  having been closed (for instance, a read() call could return some
+  previously buffered data). Patch by Dmitry Vasiliev.
+
 - Issue #4705: Fix the -u ("unbuffered binary stdout and stderr") command-line
   flag to work properly. Furthermore, when specifying -u, the text stdout
   and stderr streams have line-by-line buffering enabled (the default being