potiuk commented on code in PR #28001:
URL: https://github.com/apache/airflow/pull/28001#discussion_r1039055381
##########
docs/apache-airflow/concepts/dynamic-task-mapping.rst:
##########
@@ -296,8 +296,93 @@ Similar to ``expand``, you can also map against a XCom
that returns a list of di
task_id="copy_files", source_bucket_name=list_filenames.bucket
).expand_kwargs(copy_kwargs)
-Filtering items from an expanded task
-=====================================
+Mapping over a task group
+=========================
+
+Similar to a TaskFlow task, you can also call either ``expand`` or
``expand_kwargs`` on a ``@task_group``-decorated function to create a mapped
task group:
+
+.. note:: Implementations of individual tasks in this section are omitted for
brevity.
+
+.. code-block:: python
+
+ @task_group
+ def file_transforms(filename):
+ return convert_to_yaml(filename)
+
+
+ file_transforms.expand(filename=["data1.json", "data2.json"])
+
+In the above example, task ``convert_to_yaml`` is expanded into two task
instances at runtime. The first expanded would receive ``"data1.json"`` as
input, and the second ``"data2.json"``.
+
+.. note:: Arguments passed to a mapped task group is a proxy, not real values
+
+ Different from task functions (``@task``), a task group function is
evaluated eagerly, and only once when the DAG is parsed. This means that
parameters passed into the function is only a placeholder, and not a real
value. For example, this will *not* work:
Review Comment:
Agree. The whole documentation update is great. It's hard to explain it
cleared, but maybe siimply state (instead of `eagerly` that it is evaluated
during parsing, in the scheduler and not during exection in worker?
That could help understand what's going on.
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