Make sure you have checked _all_ steps below. ### Jira
- [x] My PR addresses the following [Airflow Jira](https://issues.apache.org/jira/browse/AIRFLOW/) issues and references them in the PR title. For example, "\[AIRFLOW-XXX\] My Airflow PR" - https://issues.apache.org/jira/browse/AIRFLOW-3006 - In case you are fixing a typo in the documentation you can prepend your commit with \[AIRFLOW-XXX\], code changes always need a Jira issue. ### Description - [x] Here are some details about my PR, including screenshots of any UI changes: When `schedule_interval` is set to `"None"` (Not python literal `None` but 'None' string) as shown in the example below: ```python dag = DAG('params-temp3', default_args=default_args, schedule_interval='None') ``` it gives the following error: ```python [2018-09-04 23:26:21,515] {dag_processing.py:582} INFO - Started a process (PID: 65903) to generate tasks for /Users/kaxil/airflow/dags/params-temp1.py Process DagFileProcessor386-Process: Traceback (most recent call last): File "/Users/kaxil/anaconda2/lib/python2.7/multiprocessing/process.py", line 267, in _bootstrap self.run() File "/Users/kaxil/anaconda2/lib/python2.7/multiprocessing/process.py", line 114, in run self._target(*self._args, **self._kwargs) File "/Users/kaxil/.virtualenvs/tst-pip-airflow/lib/python2.7/site-packages/airflow/jobs.py", line 388, in helper pickle_dags) File "/Users/kaxil/.virtualenvs/tst-pip-airflow/lib/python2.7/site-packages/airflow/utils/db.py", line 74, in wrapper return func(*args, **kwargs) File "/Users/kaxil/.virtualenvs/tst-pip-airflow/lib/python2.7/site-packages/airflow/jobs.py", line 1832, in process_file self._process_dags(dagbag, dags, ti_keys_to_schedule) File "/Users/kaxil/.virtualenvs/tst-pip-airflow/lib/python2.7/site-packages/airflow/jobs.py", line 1422, in _process_dags dag_run = self.create_dag_run(dag) File "/Users/kaxil/.virtualenvs/tst-pip-airflow/lib/python2.7/site-packages/airflow/utils/db.py", line 74, in wrapper return func(*args, **kwargs) File "/Users/kaxil/.virtualenvs/tst-pip-airflow/lib/python2.7/site-packages/airflow/jobs.py", line 856, in create_dag_run next_run_date = dag.normalize_schedule(min(task_start_dates)) File "/Users/kaxil/.virtualenvs/tst-pip-airflow/lib/python2.7/site-packages/airflow/models.py", line 3410, in normalize_schedule following = self.following_schedule(dttm) File "/Users/kaxil/.virtualenvs/tst-pip-airflow/lib/python2.7/site-packages/airflow/models.py", line 3353, in following_schedule cron = croniter(self._schedule_interval, dttm) File "/Users/kaxil/.virtualenvs/tst-pip-airflow/lib/python2.7/site-packages/croniter/croniter.py", line 92, in __init__ self.expanded, self.nth_weekday_of_month = self.expand(expr_format) File "/Users/kaxil/.virtualenvs/tst-pip-airflow/lib/python2.7/site-packages/croniter/croniter.py", line 467, in expand raise CroniterBadCronError(cls.bad_length) CroniterBadCronError: Exactly 5 or 6 columns has to be specified for iteratorexpression. [2018-09-04 23:26:22,657] {dag_processing.py:495} INFO - Processor for /Users/kaxil/airflow/dags/params-temp1.py finished ``` Our documentation at https://airflow.apache.org/scheduler.html#dag-runs has 'None' as **preset** since 1.8.2 or even before, hence we should accept **"None"** as a valid `schedule_interval` apart from **None** ### Tests - [x] My PR adds the following unit tests __OR__ does not need testing for this extremely good reason: - `test_scheduler_dagrun_none ` ### Commits - [x] My commits all reference Jira issues in their subject lines, and I have squashed multiple commits if they address the same issue. In addition, my commits follow the guidelines from "[How to write a good git commit message](http://chris.beams.io/posts/git-commit/)": 1. Subject is separated from body by a blank line 1. Subject is limited to 50 characters (not including Jira issue reference) 1. Subject does not end with a period 1. Subject uses the imperative mood ("add", not "adding") 1. Body wraps at 72 characters 1. Body explains "what" and "why", not "how" ### Documentation - [x] In case of new functionality, my PR adds documentation that describes how to use it. - When adding new operators/hooks/sensors, the autoclass documentation generation needs to be added. ### Code Quality - [x] Passes `git diff upstream/master -u -- "*.py" | flake8 --diff` [ Full content available at: https://github.com/apache/incubator-airflow/pull/3846 ] This message was relayed via gitbox.apache.org for [email protected]
