(airflow) branch main updated: Fix reversed direction examples in FanOutMapper docs (#69313)

[weilee]

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Lee-W pushed a commit to branch main
in repository https://gitbox.apache.org/repos/asf/airflow.git


The following commit(s) were added to refs/heads/main by this push:
     new 73113791694 Fix reversed direction examples in FanOutMapper docs 
(#69313)
73113791694 is described below

commit 7311379169462a12caad0f0ae64fbbae13b49b12
Author: Wei Lee <weilee...@gmail.com>
AuthorDate: Tue Jul 7 12:12:41 2026 +0800

    Fix reversed direction examples in FanOutMapper docs (#69313)
---
 airflow-core/src/airflow/partition_mappers/temporal.py    | 12 +++++++-----
 .../airflow/sdk/definitions/partition_mappers/temporal.py | 15 +++++++++------
 2 files changed, 16 insertions(+), 11 deletions(-)

diff --git a/airflow-core/src/airflow/partition_mappers/temporal.py 
b/airflow-core/src/airflow/partition_mappers/temporal.py
index 1938a18f84d..c16801c97b1 100644
--- a/airflow-core/src/airflow/partition_mappers/temporal.py
+++ b/airflow-core/src/airflow/partition_mappers/temporal.py
@@ -469,9 +469,11 @@ class FanOutMapper(PartitionMapper):
     is N→1 (downstream waits until all members arrive), fan-out is 1→N (one
     upstream event creates one downstream Dag run per member).
 
-    For forward fan-out (emit the trailing period ending at the upstream key,
-    instead of the period it represents), pass 
``direction=Window.Direction.FORWARD``
-    to the window:
+    ``window``'s direction controls which period each upstream key fans out to.
+    The default, ``Window.Direction.FORWARD``, yields the period *starting at*
+    the upstream key (the period it represents); ``Window.Direction.BACKWARD``
+    yields the trailing period *ending at* the upstream key. Pass
+    ``direction=Window.Direction.BACKWARD`` to the window for the latter:
 
     .. code-block:: python
 
@@ -482,8 +484,8 @@ class FanOutMapper(PartitionMapper):
         FanOutMapper(upstream_mapper=StartOfWeekMapper(), window=WeekWindow())
 
         # Weekly upstream → the 7 days ending at the upstream Monday (trailing 
period)
-        forward_window = WeekWindow(direction=Window.Direction.FORWARD)
-        FanOutMapper(upstream_mapper=StartOfWeekMapper(), 
window=forward_window)
+        backward_window = WeekWindow(direction=Window.Direction.BACKWARD)
+        FanOutMapper(upstream_mapper=StartOfWeekMapper(), 
window=backward_window)
     """
 
     # Keep ``FanOutMapper.default_downstream_mapper_by_window_name`` in sync 
with
diff --git a/task-sdk/src/airflow/sdk/definitions/partition_mappers/temporal.py 
b/task-sdk/src/airflow/sdk/definitions/partition_mappers/temporal.py
index 0cf0a705d5c..ccb1497f032 100644
--- a/task-sdk/src/airflow/sdk/definitions/partition_mappers/temporal.py
+++ b/task-sdk/src/airflow/sdk/definitions/partition_mappers/temporal.py
@@ -137,20 +137,23 @@ class FanOutMapper(PartitionMapper):
     waits for all members), fan-out is 1→N (one upstream event creates many
     downstream Dag runs).
 
-    For forward fan-out (emit the *next* period's members instead of the 
current
-    one), pass ``direction=Window.Direction.FORWARD`` to the window:
+    ``window``'s direction controls which period each upstream key fans out to.
+    The default, ``Window.Direction.FORWARD``, yields the period *starting at*
+    the upstream key (the period it represents); ``Window.Direction.BACKWARD``
+    yields the trailing period *ending at* the upstream key. Pass
+    ``direction=Window.Direction.BACKWARD`` to the window for the latter:
 
     .. code-block:: python
 
         from airflow.sdk import WeekWindow, Window
         from airflow.sdk.definitions.partition_mappers.temporal import 
FanOutMapper, StartOfWeekMapper
 
-        # Weekly upstream → 7 daily downstream Dag runs (current week)
+        # Weekly upstream → 7 daily downstream Dag runs (the 7 days the 
upstream Monday represents)
         FanOutMapper(upstream_mapper=StartOfWeekMapper(), window=WeekWindow())
 
-        # Weekly upstream → 7 daily keys for the *following* week
-        forward_window = WeekWindow(direction=Window.Direction.FORWARD)
-        FanOutMapper(upstream_mapper=StartOfWeekMapper(), 
window=forward_window)
+        # Weekly upstream → the 7 days ending at the upstream Monday (trailing 
period)
+        backward_window = WeekWindow(direction=Window.Direction.BACKWARD)
+        FanOutMapper(upstream_mapper=StartOfWeekMapper(), 
window=backward_window)
     """
 
     # Keep ``FanOutMapper.default_downstream_mapper_by_window_name`` in sync 
with