potiuk commented on a change in pull request #4779: [AIRFLOW-3958] List tasks
upstream work in chain
URL: https://github.com/apache/airflow/pull/4779#discussion_r283636335
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File path: airflow/utils/helpers.py
##########
@@ -150,19 +150,40 @@ def as_flattened_list(iterable):
def chain(*tasks):
- """
+ r"""
Given a number of tasks, builds a dependency chain.
+ Support mix airflow.models.BaseOperator and
List[airflow.models.BaseOperator].
+ If you want to chain between two List[airflow.models.BaseOperator], have to
+ make sure they have same length.
- chain(task_1, task_2, task_3, task_4)
+ chain(t1, [t2, t3], [t4, t5], t6)
is equivalent to
- task_1.set_downstream(task_2)
- task_2.set_downstream(task_3)
- task_3.set_downstream(task_4)
+ / -> t2 -> t4 \
+ t1 -> t6
+ \ -> t3 -> t5 /
+
+ t1.set_downstream(t2)
+ t1.set_downstream(t3)
+ t2.set_downstream(t4)
+ t3.set_downstream(t5)
+ t4.set_downstream(t6)
+ t5.set_downstream(t6)
+
+ :param tasks: List of tasks or List[airflow.models.BaseOperator] to set
dependencies
+ :type tasks: List[airflow.models.BaseOperator] or
airflow.models.BaseOperator
"""
- for up_task, down_task in zip(tasks[:-1], tasks[1:]):
- up_task.set_downstream(down_task)
+ from airflow.models import BaseOperator
+ for index, up_task in enumerate(tasks[:-1]):
+ down_task = tasks[index + 1]
+ if isinstance(up_task, BaseOperator):
+ up_task.set_downstream(down_task)
+ elif isinstance(down_task, BaseOperator):
+ down_task.set_upstream(up_task)
+ else:
Review comment:
We should check here that these are both iterables and that they have the
same length (and throw exception otherwise).
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