Re: [PR] [SPARK-55224][PYTHON] Use Spark DataType as ground truth in Pandas-Arrow serialization [spark]

["Yicong-Huang (via GitHub)" <gi...@apache.org>]

Yicong-Huang commented on code in PR #53992:
URL: https://github.com/apache/spark/pull/53992#discussion_r2751868045


##########
python/pyspark/sql/pandas/serializers.py:
##########
@@ -409,21 +414,21 @@ def arrow_to_pandas(
             ndarray_as_list=ndarray_as_list,
         )
 
-    def _create_array(self, series, arrow_type, spark_type=None, arrow_cast=False):
+    def _create_array(self, series, spark_type, *, arrow_cast=False, prefers_large_types=False):
         """
-        Create an Arrow Array from the given pandas.Series and optional type.
+        Create an Arrow Array from the given pandas.Series and Spark type.
 
         Parameters
         ----------
         series : pandas.Series
             A single series
-        arrow_type : pyarrow.DataType, optional
-            If None, pyarrow's inferred type will be used
         spark_type : DataType, optional
-            If None, spark type converted from arrow_type will be used
-        arrow_cast: bool, optional
+            The Spark type to use. If None, pyarrow's inferred type will be used.

Review Comment:
   `createDataFrame ([conversion.py](https://github.com/apache/spark/blob/master/python/pyspark/sql/pandas/conversion.py#L868-L872), [connect/session.py](https://github.com/apache/spark/blob/master/python/pyspark/sql/connect/session.py#L615-L627))`: `spark_type` can be `None` for non-timestamp columns when user doesn't provide a schema. This is existing behavior on master:
   
   ```
   spark_types = [
       TimestampType() if is_datetime64_dtype(t) ...
       else None  # Non-timestamp columns get None
       for t in data.dtypes
   ]
   ```
   
   And later [when the type is None](https://github.com/apache/spark/blob/master/python/pyspark/sql/pandas/serializers.py#L474-L476) (in this case, both spark type and arrow type will be None in master), pyarrow will [try to infer](https://arrow.apache.org/docs/python/generated/pyarrow.Array.html#pyarrow.Array.from_pandas).
   
   ```
   return pa.Array.from_pandas(
       series, mask=mask, type=None, safe=self._safecheck
   )
   ```
   
   ```
   > type : pyarrow.DataType, optional
   > If not provided, the Arrow type is inferred from the pandas dtype.
   ```
   
   



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