[GitHub] [airflow] uranusjr commented on a change in pull request #18471: Improve error message for BranchPythonOperator when no task_id to follow

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uranusjr commented on a change in pull request #18471:
URL: https://github.com/apache/airflow/pull/18471#discussion_r715463290



##########
File path: airflow/operators/python.py
##########
@@ -178,6 +178,8 @@ class BranchPythonOperator(PythonOperator, SkipMixin):
 
     def execute(self, context: Dict):
         branch = super().execute(context)
+        if branch is None:
+            raise AirflowException("Branch callable must return at least one task_id to follow")

Review comment:
       Kind of wondering whether we should check for all non-str values. Or even check the value is a valid task ID? Something like…
   
   ```python
   if isinstance(branch, str):
       branches = [branch]
   try:
       branches = list(branch)  # Check iterability.
   except TypeError:
       raise AirflowException("Branch callable must return either a task ID or a list of IDs")
   valid_task_ids = set(context["context"].task_ids)
   if not any(b in valid_task_ids for b in branches):
       raise AirflowException("Branch callable must return at least one task ID to follow")
   ```




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