gaogaotiantian commented on code in PR #57099:
URL: https://github.com/apache/spark/pull/57099#discussion_r3562024514
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python/pyspark/sql/conversion.py:
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@@ -980,6 +1017,64 @@ class ArrowTableToRowsConversion:
Conversion from Arrow Table to Rows.
"""
+ @staticmethod
+ def _to_pylist(column: Union["pa.Array", "pa.ChunkedArray"]) -> List[Any]:
+ """
+ Equivalent to ``column.to_pylist()``, but converts (nested) list
columns in bulk
+ instead of one scalar at a time.
+
+ ``Array.to_pylist()`` materializes one Scalar per element; for list
types each row
+ additionally allocates a C++ scalar, a Python Scalar wrapper and a
Python Array
+ wrapper for the row's values before converting elements one by one,
which is
+ several times slower than converting the flattened child values in a
single pass
+ and slicing the resulting Python list per row (see
apache/arrow#50326). The values
+ themselves are still converted by Arrow's own ``to_pylist``, so
results are exactly
+ identical: ``None`` stays ``None`` and values inside numeric lists
stay Python ints,
+ unlike a pandas round trip which would coerce them to floats/NaN.
NumPy is used
+ only for the offsets (non-null integers) and the validity bitmap
(booleans), so no
+ value coercion can occur.
+
+ This can be removed once the minimum supported PyArrow version
includes the fix
+ for apache/arrow#50326.
+ """
+ import pyarrow as pa
+ import pyarrow.types as pa_types
+
+ if _has_fast_native_to_pylist() or not _is_numpy_available():
+ # Recent PyArrow converts without per-element Scalars natively
+ # (apache/arrow#50326); without NumPy the bulk paths below are
+ # unavailable. Either way, use the native conversion.
+ return column.to_pylist()
+
+ if isinstance(column, pa.ChunkedArray):
+ result: List[Any] = []
+ for chunk in column.chunks:
+ result.extend(ArrowTableToRowsConversion._to_pylist(chunk))
+ return result
+
+ column_type = column.type
Review Comment:
I meant assigning `column.type` to `column_type`. I think it's also some
optimization that tries to save attribute access cost.
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