TheNeuralBit commented on a change in pull request #14135:
URL: https://github.com/apache/beam/pull/14135#discussion_r591984316
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File path: sdks/python/apache_beam/dataframe/expressions.py
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@@ -312,6 +352,11 @@ def __init__(
requires_partition_by: The required (common) partitioning of the args.
preserves_partition_by: The level of partitioning preserved.
"""
+ assert preserves_partition_by != partitionings.Nothing(), (
+ "Preserving Nothing() partitioning is not allowed. Any expression "
+ "can trivially preserve at least Singleton() partitioning. If you "
+ "intend to indicate this expression can preserve _any_ partioning, use
"
+ "Index() instead.")
Review comment:
Done
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