airflow - key 错误 : 'ti' in Apache Airflow xcom

Question

我们正在尝试运行一个带有 2 个任务的简单 DAG，这些任务将通过 xcom 进行数据通信。

DAG 文件:

from __future__ import print_function
import airflow
from airflow import DAG
from airflow.operators.bash_operator import BashOperator
from airflow.operators.python_operator import PythonOperator

args = {
    'owner': 'airflow',
    'start_date': airflow.utils.dates.days_ago(2)
}

dag = DAG(
    'example_xcom',
    schedule_interval="@once",
    default_args=args)

value_1 = [1, 2, 3]


def push(**kwargs):
    # pushes an XCom without a specific target
    kwargs['ti'].xcom_push(key='value from pusher 1', value=value_1)


def puller(**kwargs):
    ti = kwargs['ti']

    v1 = ti.xcom_pull(key=None, task_ids='push')
    assert v1 == value_1

    v1 = ti.xcom_pull(key=None, task_ids=['push'])
    assert (v1) == (value_1)


push1 = PythonOperator(
    task_id='push', dag=dag, python_callable=push)

pull = BashOperator(
    task_id='also_run_this',
    bash_command='echo {{ ti.xcom_pull(task_ids="push_by_returning") }}',
    dag=dag)

pull.set_upstream(push1)

但是在 Airflow 中运行 DAG 时，我们遇到了以下异常。

[2018-09-27 16:55:33,431] {base_task_runner.py:98} INFO - Subtask: [2018-09-27 16:55:33,430] {models.py:189} INFO - Filling up the DagBag from /home/airflow/gcs/dags/xcom.py
[2018-09-27 16:55:33,694] {base_task_runner.py:98} INFO - Subtask: Traceback (most recent call last):
[2018-09-27 16:55:33,694] {base_task_runner.py:98} INFO - Subtask:   File "/usr/local/bin/airflow", line 27, in <module>
[2018-09-27 16:55:33,696] {base_task_runner.py:98} INFO - Subtask:     args.func(args)
[2018-09-27 16:55:33,697] {base_task_runner.py:98} INFO - Subtask:   File "/usr/local/lib/python2.7/site-packages/airflow/bin/cli.py", line 392, in run
[2018-09-27 16:55:33,697] {base_task_runner.py:98} INFO - Subtask:     pool=args.pool,
[2018-09-27 16:55:33,698] {base_task_runner.py:98} INFO - Subtask:   File "/usr/local/lib/python2.7/site-packages/airflow/utils/db.py", line 50, in wrapper
[2018-09-27 16:55:33,699] {base_task_runner.py:98} INFO - Subtask:     result = func(*args, **kwargs)
[2018-09-27 16:55:33,699] {base_task_runner.py:98} INFO - Subtask:   File "/usr/local/lib/python2.7/site-packages/airflow/models.py", line 1492, in _run_raw_task
[2018-09-27 16:55:33,701] {base_task_runner.py:98} INFO - Subtask:     result = task_copy.execute(context=context)
[2018-09-27 16:55:33,701] {base_task_runner.py:98} INFO - Subtask:   File "/usr/local/lib/python2.7/site-packages/airflow/operators/python_operator.py", line 89, in execute
[2018-09-27 16:55:33,702] {base_task_runner.py:98} INFO - Subtask:     return_value = self.execute_callable()
[2018-09-27 16:55:33,703] {base_task_runner.py:98} INFO - Subtask:   File "/usr/local/lib/python2.7/site-packages/airflow/operators/python_operator.py", line 94, in execute_callable
[2018-09-27 16:55:33,703] {base_task_runner.py:98} INFO - Subtask:     return self.python_callable(*self.op_args, **self.op_kwargs)
[2018-09-27 16:55:33,704] {base_task_runner.py:98} INFO - Subtask:   File "/home/airflow/gcs/dags/xcom.py", line 22, in push
[2018-09-27 16:55:33,707] {base_task_runner.py:98} INFO - Subtask:     kwargs['ti'].xcom_push(key='value from pusher 1', value=value_1)
[2018-09-27 16:55:33,708] {base_task_runner.py:98} INFO - Subtask: KeyError: 'ti'

我们验证了 DAG 存在但没有问题，请帮助我们解决此问题。

Answer 1

添加 provide_context: True默认参数。这需要define **kwargs .

args = {
    'owner': 'airflow',
    'start_date': airflow.utils.dates.days_ago(2),
    'provide_context': True
}

provide_context (bool) – if set to true, Airflow will pass a set of keyword arguments that can be used in your function. This set of kwargs correspond exactly to what you can use in your jinja templates. For this to work, you need to define **kwargs in your function header.