Implement TimerHandle.when() (GH-5473) (GH-5480)

(cherry picked from commit 3d4dbd8f)
Co-authored-by: Andrew Svetlov <andrew.svetlov@gmail.com>

Doc/library/asyncio-eventloop.rst

@@ -171,7 +171,7 @@ a different clock than :func:`time.time`.
    Arrange for the *callback* to be called after the given *delay*
    seconds (either an int or float).
 
-   An instance of :class:`asyncio.Handle` is returned, which can be
+   An instance of :class:`asyncio.TimerHandle` is returned, which can be
    used to cancel the callback.
 
    *callback* will be called exactly once per call to :meth:`call_later`.
@@ -193,7 +193,7 @@ a different clock than :func:`time.time`.
 
    This method's behavior is the same as :meth:`call_later`.
 
-   An instance of :class:`asyncio.Handle` is returned, which can be
+   An instance of :class:`asyncio.TimerHandle` is returned, which can be
    used to cancel the callback.
 
    :ref:`Use functools.partial to pass keywords to the callback
@@ -1076,8 +1076,7 @@ Handle
 .. class:: Handle
 
    A callback wrapper object returned by :func:`AbstractEventLoop.call_soon`,
-   :func:`AbstractEventLoop.call_soon_threadsafe`, :func:`AbstractEventLoop.call_later`,
-   and :func:`AbstractEventLoop.call_at`.
+   :func:`AbstractEventLoop.call_soon_threadsafe`.
 
    .. method:: cancel()
 
@@ -1090,6 +1089,22 @@ Handle
 
       .. versionadded:: 3.7
 
+.. class:: TimerHandle
+
+   A callback wrapper object returned by :func:`AbstractEventLoop.call_later`,
+   and :func:`AbstractEventLoop.call_at`.
+
+   The class is inherited from :class:`Handle`.
+
+   .. method:: when()
+
+      Return a scheduled callback time as :class:`float` seconds.
+
+      The time is an absolute timestamp, using the same time
+      reference as :meth:`AbstractEventLoop.time`.
+
+      .. versionadded:: 3.7
+
 
 SendfileNotAvailableError
 -------------------------

Lib/asyncio/events.py

@@ -156,6 +156,14 @@ class TimerHandle(Handle):
             self._loop._timer_handle_cancelled(self)
         super().cancel()
 
+    def when(self):
+        """Return a scheduled callback time.
+
+        The time is an absolute timestamp, using the same time
+        reference as loop.time().
+        """
+        return self._when
+
 
 class AbstractServer:
     """Abstract server returned by create_server()."""

Lib/test/test_asyncio/test_events.py

@@ -2679,6 +2679,12 @@ class TimerTests(unittest.TestCase):
                                 mock.Mock())
         self.assertEqual(hash(h), hash(when))
 
+    def test_when(self):
+        when = time.monotonic()
+        h = asyncio.TimerHandle(when, lambda: False, (),
+                                mock.Mock())
+        self.assertEqual(when, h.when())
+
     def test_timer(self):
         def callback(*args):
             return args

Misc/NEWS.d/next/Library/2018-02-01-17-54-08.bpo-32741.KUvOPL.rst

+Implement ``asyncio.TimerHandle.when()`` method.