Re: [PR] [SPARK-55299][PS] Infer the correct unit for calculated timedeltas [spark]

["uros-b (via GitHub)" <gi...@apache.org>]

uros-b commented on code in PR #56624:
URL: https://github.com/apache/spark/pull/56624#discussion_r3444997977


##########
python/pyspark/pandas/data_type_ops/timedelta_ops.py:
##########
@@ -72,6 +73,35 @@ def restore(self, col: pd.Series) -> pd.Series:
         else:
             return col.astype(self.dtype)
 
+    def _with_inferred_unit(
+        self, result: SeriesOrIndex, left: IndexOpsLike, right: Union[IndexOpsMixin, timedelta]
+    ) -> SeriesOrIndex:
+        # pandas 3.0.0+ promotes timedelta arithmetic to the finer resolution of the
+        # operands; before that timedelta64 is always nanoseconds.

Review Comment:
   The last part is a bit imprecisely worded. pandas 2.0 introduced non-nanosecond resolution, so timedelta64[s]/[ms]/[us] have existed in plain pandas since well before 3.0.0.
   
   Perhaps a better note would be `; before that, pandas-on-Spark represented timedelta as nanoseconds.`.



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