add comment to clarify error handling in next method of PyRecordBatchStream

Author: kosiew

src/record_batch.rs

@@ -63,9 +63,13 @@ impl PyRecordBatchStream {
 impl PyRecordBatchStream {
     fn next(&mut self, py: Python) -> PyResult<PyRecordBatch> {
         let stream = self.stream.clone();
-        wait_for_future(py, next_stream(stream, true))?
+        // Two-step error handling process:
+        // 1. First ? handles errors from the async runtime/future execution
+        let item = wait_for_future(py, next_stream(stream, true))?;
+        // 2. Second ? converts and propagates any DataFusion errors to Python errors
+        let batch = item.map_err(PyDataFusionError::from)?;
+        Ok(batch)
     }
-
     fn __next__(&mut self, py: Python) -> PyResult<PyRecordBatch> {
         self.next(py)
     }