Issue #5506: BytesIO objects now have a getbuffer() method exporting a
view of their contents without duplicating them.  The view is both readable
and writable.
diff --git a/Lib/_pyio.py b/Lib/_pyio.py
index 12ae4b6..6b25640 100644
--- a/Lib/_pyio.py
+++ b/Lib/_pyio.py
@@ -785,6 +785,11 @@
             raise ValueError("getvalue on closed file")
         return bytes(self._buffer)
 
+    def getbuffer(self):
+        """Return a readable and writable view of the buffer.
+        """
+        return memoryview(self._buffer)
+
     def read(self, n=None):
         if self.closed:
             raise ValueError("read from closed file")