bpo-18748: Fix _pyio.IOBase destructor (closed case) (GH-13952)

_pyio.IOBase destructor now does nothing if getting the closed
attribute fails to better mimick _io.IOBase finalizer.

Author: vstinner

Lib/_pyio.py

@@ -405,6 +405,16 @@ def close(self):
 
     def __del__(self):
         """Destructor.  Calls close()."""
+        try:
+            closed = self.closed
+        except Exception:
+            # If getting closed fails, then the object is probably
+            # in an unusable state, so ignore.
+            return
+
+        if closed:
+            return
+
         if _IOBASE_EMITS_UNRAISABLE:
             self.close()
         else:

Misc/NEWS.d/next/Library/2019-06-11-01-54-19.bpo-18748.ADqCkq.rst

@@ -0,0 +1,2 @@
+:class:`_pyio.IOBase` destructor now does nothing if getting the ``closed``
+attribute fails to better mimick :class:`_io.IOBase` finalizer.