fix: consider #NUM! error type as None (#321)

* consider `#NUM!` error type as `None`

* Update python/tests/test_fastexcel.py

Co-authored-by: Luka Peschke <mail@lukapeschke.com>

Author: sphuber

python/tests/fixtures/fixture-invalid-cell-value-num.xlsx

@@ -533,6 +533,15 @@ def test_null_values_in_cells() -> None:
     pd_assert_frame_equal(sheet.to_pandas(), pd_expected)
 
 
+def test_invalid_value_num() -> None:
+    excel_reader = fastexcel.read_excel(path_for_fixture("fixture-invalid-cell-value-num.xlsx"))
+    sheet = excel_reader.load_sheet(0)
+
+    expected = {"Column": [8.0, None]}
+    pd_assert_frame_equal(sheet.to_pandas(), pd.DataFrame(expected))
+    pl_assert_frame_equal(sheet.to_polars(), pl.DataFrame(expected))
+
+
 def test_null_column_is_nullable() -> None:
     sheet = fastexcel.read_excel(path_for_fixture("null-column.xlsx")).load_sheet(0)
     assert sheet.to_arrow().schema.field("nullonly").nullable is True

python/tests/test_fastexcel.py

@@ -229,7 +229,7 @@ fn get_cell_dtype<DT: CellType + Debug + DataType>(
         match cell.get_error() {
             // considering cells with #N/A! or #REF! as null
             Some(
-                CellErrorType::NA | CellErrorType::Value | CellErrorType::Null | CellErrorType::Ref,
+                CellErrorType::NA | CellErrorType::Value | CellErrorType::Null | CellErrorType::Ref | CellErrorType::Num,
             ) => Ok(DType::Null),
             Some(err) => Err(FastExcelErrorKind::CalamineCellError(err.to_owned()).into()),
             None => Err(FastExcelErrorKind::Internal(format!(