Issue #13872: socket.detach() now marks the socket closed (as mirrored in the socket repr()).
Patch by Matt Joiner.
diff --git a/Lib/socket.py b/Lib/socket.py
index 1e28549..a93cd11 100644
--- a/Lib/socket.py
+++ b/Lib/socket.py
@@ -197,6 +197,17 @@
         if self._io_refs <= 0:
             self._real_close()
 
+    def detach(self):
+        """detach() -> file descriptor
+
+        Close the socket object without closing the underlying file descriptor.
+        The object cannot be used after this call, but the file descriptor
+        can be reused for other purposes.  The file descriptor is returned.
+        """
+        self._closed = True
+        return super().detach()
+
+
 def fromfd(fd, family, type, proto=0):
     """ fromfd(fd, family, type[, proto]) -> socket object
 
diff --git a/Lib/test/test_socket.py b/Lib/test/test_socket.py
index d77b7dc..cce0d1b 100644
--- a/Lib/test/test_socket.py
+++ b/Lib/test/test_socket.py
@@ -951,6 +951,7 @@
         f = self.cli_conn.detach()
         self.assertEqual(f, fileno)
         # cli_conn cannot be used anymore...
+        self.assertTrue(self.cli_conn._closed)
         self.assertRaises(socket.error, self.cli_conn.recv, 1024)
         self.cli_conn.close()
         # ...but we can create another socket using the (still open)