kylebarron commented on code in PR #1222:
URL:
https://github.com/apache/datafusion-python/pull/1222#discussion_r2319615655
##########
python/datafusion/dataframe.py:
##########
@@ -1098,21 +1102,42 @@ def unnest_columns(self, *columns: str, preserve_nulls:
bool = True) -> DataFram
return DataFrame(self.df.unnest_columns(columns,
preserve_nulls=preserve_nulls))
def __arrow_c_stream__(self, requested_schema: object | None = None) ->
object:
- """Export an Arrow PyCapsule Stream.
+ """Export the DataFrame as an Arrow C Stream.
- This will execute and collect the DataFrame. We will attempt to
respect the
- requested schema, but only trivial transformations will be applied
such as only
- returning the fields listed in the requested schema if their data
types match
- those in the DataFrame.
+ The DataFrame is executed using DataFusion's streaming APIs and
exposed via
+ Arrow's C Stream interface. Record batches are produced incrementally,
so the
+ full result set is never materialized in memory. When
``requested_schema`` is
+ provided, only straightforward projections such as column selection or
+ reordering are applied.
Args:
requested_schema: Attempt to provide the DataFrame using this
schema.
Returns:
- Arrow PyCapsule object.
+ Arrow PyCapsule object representing an ``ArrowArrayStream``.
"""
+ # ``DataFrame.__arrow_c_stream__`` in the Rust extension leverages
+ # ``execute_stream_partitioned`` under the hood to stream batches while
+ # preserving the original partition order.
return self.df.__arrow_c_stream__(requested_schema)
+ def __iter__(self) -> Iterator[pa.RecordBatch]:
Review Comment:
`RecordBatchStream` already has `__iter__` and `__aiter__` methods
https://datafusion.apache.org/python/autoapi/datafusion/record_batch/index.html#datafusion.record_batch.RecordBatchStream
Can we just have a method that converts a `DataFrame` into a
`RecordBatchStream`? Then an `__iter__` on `DataFrame` would just convert to a
`RecordBatchStream` under the hood.
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