ashb commented on code in PR #22849:
URL: https://github.com/apache/airflow/pull/22849#discussion_r846319944
##########
airflow/models/taskinstance.py:
##########
@@ -295,6 +299,58 @@ def clear_task_instances(
dr.start_date = None
+class _LazyXComAccessIterator(collections.abc.Iterator):
+ def __init__(self, cm: ContextManager[Query]):
+ self._cm = cm
+ self._it = iter(cm.__enter__())
+
+ def __del__(self):
+ self._cm.__exit__()
+
+ def __iter__(self):
+ return self
+
+ def __next__(self):
+ return XCom.deserialize_value(next(self._it))
+
+
+class _LazyXComAccess(collections.abc.Sequence):
+ """Wrapper to lazily pull XCom with a sequence-like interface.
+
+ Note that since the session bound to the parent query may have died when we
+ actually access the sequence's content, we must create a new fresh session
+ for every function call with ``with_session()``.
+ """
+
+ def __init__(self, query: Query):
+ self._q = query
+
+ def __len__(self):
+ with self._get_bound_query() as query:
+ return query.count()
+
+ def __iter__(self):
+ return _LazyXComAccessIterator(self._get_bound_query())
Review Comment:
Oh nice, this means we can iterate over the list multiple times in a
consuming task. Makes the docs easier to write.
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