client: implement the fileno() method

alsa_midi/client.py

@@ -404,6 +404,7 @@ def close(self):
         self._handle_p = None  # type: ignore
         self.handle = None  # type: ignore
         self._event_parser = None
+        self._fd = -1
 
     def _get_fds(self):
         """Get the file descriptor number for the client connection into :data:`self._fd`."""
@@ -430,6 +431,21 @@ def _get_event_parser(self):
             self._event_parser = parser
         return parser
 
+    def fileno(self):
+        """Return file descriptor assigned to this connection.
+
+        This file descriptor can be used with select, poll, or other event
+        loop mechanisms for monitoring ALSA sequencer events.
+
+        Wraps :alsa:`snd_seq_poll_descriptors`.
+
+        :return: file descriptor number
+        :raises OSError: if the connection is closed or file descriptor is not available
+        """
+        if self._fd >= 0:
+            return self._fd
+        raise OSError("File descriptor not available")
+
     def get_sequencer_name(self) -> str:
         """Get sequencer name.
 

tests/test_client.py

@@ -611,3 +611,43 @@ def test_set_client_pool_input():
     client.set_client_pool_input(200)
     pool = client.get_client_pool()
     assert pool.input_pool == 200
+
+
+@pytest.mark.require_alsa_seq
+def test_fileno():
+    client = SequencerClient("test")
+    fd = client.fileno()
+    assert isinstance(fd, int)
+    assert fd >= 0
+    client.close()
+
+
+@pytest.mark.require_alsa_seq
+def test_fileno_after_close():
+    client = SequencerClient("test")
+    fd = client.fileno()
+    assert fd >= 0
+    client.close()
+    with pytest.raises(OSError) as exc_info:
+        client.fileno()
+    assert "File descriptor not available" in str(exc_info.value)
+
+
+@pytest.mark.require_alsa_seq
+def test_fileno_async_client():
+    client = AsyncSequencerClient("test")
+    fd = client.fileno()
+    assert isinstance(fd, int)
+    assert fd >= 0
+    client.close()
+
+
+@pytest.mark.require_alsa_seq
+def test_fileno_async_client_after_close():
+    client = AsyncSequencerClient("test")
+    fd = client.fileno()
+    assert fd >= 0
+    client.close()
+    with pytest.raises(OSError) as exc_info:
+        client.fileno()
+    assert "File descriptor not available" in str(exc_info.value)