yifanmai commented on a change in pull request #13303:
URL: https://github.com/apache/beam/pull/13303#discussion_r523237999
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File path:
sdks/python/apache_beam/runners/portability/fn_api_runner/translations.py
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@@ -1212,6 +1213,22 @@ def get_ancestors(name):
return None
+def _parent_for_fused_stages(stages, context):
+ # type: (Iterable[str], TransformContext) -> Optional[str]
+
+ '''Returns the name of the new parent for the fused stages.
+
+ The new parent is the lowest common ancestor of the fused stages that is not
+ contained in the set of fused stages. The provided context is used to compute
+ ancestors of stages.
+ '''
+ result = functools.reduce(
+ lambda a, b: _lowest_common_ancestor(a, b, context), stages)
+ if result in stages:
+ result = context.parents_map().get(result)
Review comment:
Yes; if `result` was the lowest common ancestor for set S (where nodes
are ancestors of themselves), then it is impossible for `result`'s parent to
still be in S; otherwise `result` would not be an ancestor of `result`'s
parent, which is in S, which contradicts `result`'s status as lowest common
ancestor of S.
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