mik-laj commented on a change in pull request #4779: [AIRFLOW-3958] Support
list tasks as upstream in chain
URL: https://github.com/apache/airflow/pull/4779#discussion_r264079684
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File path: airflow/utils/helpers.py
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@@ -154,19 +154,32 @@ def as_flattened_list(iterable):
def chain(*tasks):
- """
- Given a number of tasks, builds a dependency chain.
+ r"""
+ Given a number of tasks or list of tasks, builds a dependency chain.
- chain(task_1, task_2, task_3, task_4)
+ chain(task_1, [task_2, task_3], task_4, task_5)
is equivalent to
+ / --> task_2 \
+ task_1 --> task_4 --> task_5
+ \ --> task_3 /
+
task_1.set_downstream(task_2)
- task_2.set_downstream(task_3)
+ task_1.set_downstream(task_3)
+ task_2.set_downstream(task_4)
task_3.set_downstream(task_4)
+ task_4.set_downstream(task_5)
+
+ :param tasks: tasks or list of tasks
+ :type tasks: airflow.models.BaseOperator
"""
for up_task, down_task in zip(tasks[:-1], tasks[1:]):
- up_task.set_downstream(down_task)
+ if isinstance(up_task, list):
Review comment:
Is this necessary? According to the documentation for the `set_downstream`
method, the parameter can be both one task and a task list.
http://airflow.apache.org/code.html#airflow.models.BaseOperator.set_downstream
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