fix(python): Throw exception if dataframe is too large to be compatible with Excel

py-polars/polars/dataframe/frame.py

@@ -98,6 +98,7 @@
 from polars.dependencies import pyarrow as pa
 from polars.exceptions import (
     ColumnNotFoundError,
+    InvalidOperationError,
     ModuleUpgradeRequiredError,
     NoRowsReturnedError,
     TooManyRowsReturnedError,
@@ -3506,6 +3507,16 @@ def write_excel(
             table_start[1] + len(df.columns) - 1,
         )
 
+        excel_max_valid_rows = 1048575
+        excel_max_valid_cols = 16384
+
+        if (
+            table_finish[0] > excel_max_valid_rows
+            or table_finish[1] > excel_max_valid_cols
+        ):
+            msg = f"writing {df.height}x{df.width} frame at {position!r} does not fit worksheet dimensions of {excel_max_valid_rows} rows and {excel_max_valid_cols} columns"
+            raise InvalidOperationError(msg)
+
         # write table structure and formats into the target sheet
         if not is_empty or include_header:
             ws.add_table(

py-polars/tests/unit/io/test_spreadsheet.py

@@ -12,7 +12,10 @@
 
 import polars as pl
 import polars.selectors as cs
-from polars.exceptions import NoDataError, ParameterCollisionError
+from polars.exceptions import (
+    NoDataError,
+    ParameterCollisionError,
+)
 from polars.testing import assert_frame_equal, assert_series_equal
 from tests.unit.conftest import FLOAT_DTYPES, NUMERIC_DTYPES
 
@@ -1184,6 +1187,17 @@ def test_excel_write_worksheet_object() -> None:
             df.write_excel(None, worksheet=ws)
 
 
+def test_excel_write_beyond_max_rows_cols(tmp_path: Path) -> None:
+    tmp_path.mkdir(exist_ok=True)
+    path = tmp_path / "test_max_dimensions.xlsx"
+    sheet = "mysheet"
+
+    df = pl.DataFrame({"col1": range(10), "col2": range(10, 20)})
+
+    with pytest.raises(pl.exceptions.InvalidOperationError):
+        df.write_excel(workbook=path, worksheet=sheet, position="A1048570")
+
+
 def test_excel_freeze_panes() -> None:
     from xlsxwriter import Workbook