[PATCH libgpiod v2] bindings: python: provide fileno() for Chip and LineRequest

[Bartosz Golaszewski <brgl@xxxxxxxx>]

From: Bartosz Golaszewski <bartosz.golaszewski@xxxxxxxxxx>

Certain polling APIs in the standard library - most notably: the
select() function and the poll class - allow to poll any object that
implements the fileno() method returning the underlying file descriptor
number.

Implement fileno() for Chip and LineRequest which allows users to do:

  rd, _, _ = select([chip/request], [], [], 1)

where rd will contain the actual object passed to select which makes for
easier reading of events afterwards.

Reviewed-by: Vincent Fazio <vfazio@xxxxxxxxxxx>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@xxxxxxxxxx>
---
Changes in v2:
- Add return value type hints to test functions
- Link to v1: https://lore.kernel.org/r/20241210-python-fileno-v1-1-c811cb70e122@xxxxxxxxxx
---
 bindings/python/gpiod/chip.py             |  6 +++++
 bindings/python/gpiod/line_request.py     |  6 +++++
 bindings/python/tests/tests_edge_event.py | 37 +++++++++++++++++++++++++++++++
 bindings/python/tests/tests_info_event.py | 18 +++++++++++++++
 4 files changed, 67 insertions(+)

diff --git a/bindings/python/gpiod/chip.py b/bindings/python/gpiod/chip.py
index 30201b5..ddd07b8 100644
--- a/bindings/python/gpiod/chip.py
+++ b/bindings/python/gpiod/chip.py
@@ -344,6 +344,12 @@ class Chip:
 
         return request
 
+    def fileno(self) -> int:
+        """
+        Return the underlying file descriptor.
+        """
+        return self.fd
+
     def __repr__(self) -> str:
         """
         Return a string that can be used to re-create this chip object.
diff --git a/bindings/python/gpiod/line_request.py b/bindings/python/gpiod/line_request.py
index 9471442..ef53e16 100644
--- a/bindings/python/gpiod/line_request.py
+++ b/bindings/python/gpiod/line_request.py
@@ -224,6 +224,12 @@ class LineRequest:
 
         return cast(_ext.Request, self._req).read_edge_events(max_events)
 
+    def fileno(self) -> int:
+        """
+        Return the underlying file descriptor.
+        """
+        return self.fd
+
     def __str__(self) -> str:
         """
         Return a user-friendly, human-readable description of this request.
diff --git a/bindings/python/tests/tests_edge_event.py b/bindings/python/tests/tests_edge_event.py
index d7766ec..bf1685c 100644
--- a/bindings/python/tests/tests_edge_event.py
+++ b/bindings/python/tests/tests_edge_event.py
@@ -4,6 +4,7 @@
 import time
 from datetime import timedelta
 from functools import partial
+from select import select
 from threading import Thread
 from typing import Optional
 from unittest import TestCase
@@ -201,6 +202,42 @@ class ReadingMultipleEdgeEvents(TestCase):
             self.global_seqno += 1
 
 
+class PollLineRequestObject(TestCase):
+    def setUp(self) -> None:
+        self.sim = gpiosim.Chip(num_lines=8)
+        self.request = gpiod.request_lines(
+            self.sim.dev_path, {2: gpiod.LineSettings(edge_detection=Edge.BOTH)}
+        )
+        self.thread: Optional[Thread] = None
+
+    def tearDown(self) -> None:
+        if self.thread:
+            self.thread.join()
+            del self.thread
+        self.request.release()
+        del self.request
+        del self.sim
+
+    def trigger_rising_edge(self, offset: int) -> None:
+        time.sleep(0.05)
+        self.sim.set_pull(offset, Pull.UP)
+
+    def test_select_request_object(self) -> None:
+        self.thread = Thread(target=partial(self.trigger_rising_edge, 2))
+        self.thread.start()
+
+        rd, wr, ex = select([self.request], [], [], 1)
+        self.assertFalse(wr)
+        self.assertFalse(ex)
+        self.assertEqual(rd[0], self.request)
+
+        events = rd[0].read_edge_events()
+        self.assertEqual(len(events), 1)
+
+        event = events[0]
+        self.assertEqual(event.line_offset, 2)
+
+
 class EdgeEventStringRepresentation(TestCase):
     def test_edge_event_str(self) -> None:
         sim = gpiosim.Chip()
diff --git a/bindings/python/tests/tests_info_event.py b/bindings/python/tests/tests_info_event.py
index e726a54..31dc952 100644
--- a/bindings/python/tests/tests_info_event.py
+++ b/bindings/python/tests/tests_info_event.py
@@ -7,6 +7,7 @@ import threading
 import time
 from dataclasses import FrozenInstanceError
 from functools import partial
+from select import select
 from typing import Optional
 from unittest import TestCase
 
@@ -131,6 +132,23 @@ class WatchingInfoEventWorks(TestCase):
         self.assertGreater(ts_rel, ts_rec)
         self.assertGreater(ts_rec, ts_req)
 
+    def test_select_chip_object(self) -> None:
+        info = self.chip.watch_line_info(7)
+
+        self.thread = threading.Thread(
+            target=partial(request_reconfigure_release_line, self.sim.dev_path, 7)
+        )
+        self.thread.start()
+
+        rd, wr, ex = select([self.chip], [], [], 1)
+        self.assertFalse(wr)
+        self.assertFalse(ex)
+        self.assertEqual(rd[0], self.chip)
+
+        event = rd[0].read_info_event()
+        self.assertEqual(event.event_type, _EventType.LINE_REQUESTED)
+        self.assertEqual(event.line_info.offset, 7)
+
 
 class UnwatchingLineInfo(TestCase):
     def setUp(self) -> None:

---
base-commit: 6d9133a259e64da5e03c7e7784f0f27de7b3e59f
change-id: 20241210-python-fileno-1ed9c7bf413a

Best regards,
-- 
Bartosz Golaszewski <bartosz.golaszewski@xxxxxxxxxx>