fix(python): only raise on actual parameter collision if both "dtypes…

…" and "schema_overrides" specified for `read_excel`

py-polars/polars/exceptions.py

@@ -82,6 +82,10 @@ class NoRowsReturnedError(RowsError):
     """Exception raised when no rows are returned, but at least one row is expected."""
 
 
+class ParameterCollisionError(RuntimeError):
+    """Exception raised when the same parameter occurs multiple times."""
+
+
 class PolarsInefficientMapWarning(Warning):
     """Warning raised when a potentially slow `apply` operation is performed."""
 

py-polars/polars/io/spreadsheet/functions.py

@@ -8,7 +8,7 @@
 import polars._reexport as pl
 from polars import functions as F
 from polars.datatypes import Date, Datetime
-from polars.exceptions import NoDataError
+from polars.exceptions import NoDataError, ParameterCollisionError
 from polars.io.csv.functions import read_csv
 from polars.utils.various import normalize_filepath
 
@@ -506,13 +506,23 @@ def _csv_buffer_to_frame(
             )
         return pl.DataFrame()
 
+    if read_csv_options is None:
+        read_csv_options = {}
+    if schema_overrides:
+        if (csv_dtypes := read_csv_options.get("dtypes", {})) and set(
+            csv_dtypes
+        ).intersection(schema_overrides):
+            raise ParameterCollisionError(
+                "Cannot specify columns in both `schema_overrides` and `read_csv_options['dtypes']`"
+            )
+        read_csv_options["dtypes"] = {**csv_dtypes, **schema_overrides}
+
     # otherwise rewind the buffer and parse as csv
     csv.seek(0)
     df = read_csv(
         csv,
         separator=separator,
-        dtypes=schema_overrides,
-        **(read_csv_options or {}),
+        **read_csv_options,
     )
     return _drop_unnamed_null_columns(df)
 

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

@@ -9,7 +9,7 @@
 
 import polars as pl
 import polars.selectors as cs
-from polars.exceptions import NoDataError
+from polars.exceptions import NoDataError, ParameterCollisionError
 from polars.testing import assert_frame_equal
 
 if TYPE_CHECKING:
@@ -183,6 +183,56 @@ def test_write_excel_bytes(engine: Literal["xlsx2csv", "openpyxl"]) -> None:
     assert_frame_equal(df, df_read)
 
 
+def test_schema_overrides_11161(excel_file_path: Path) -> None:
+    df1 = pl.read_excel(
+        excel_file_path,
+        sheet_name="test4",
+        schema_overrides={"cardinality": pl.UInt16},
+    ).drop_nulls()
+    assert df1.schema == {
+        "cardinality": pl.UInt16,
+        "rows_by_key": pl.Float64,
+        "iter_groups": pl.Float64,
+    }
+
+    df2 = pl.read_excel(
+        excel_file_path,
+        sheet_name="test4",
+        read_csv_options={"dtypes": {"cardinality": pl.UInt16}},
+    ).drop_nulls()
+    assert df2.schema == {
+        "cardinality": pl.UInt16,
+        "rows_by_key": pl.Float64,
+        "iter_groups": pl.Float64,
+    }
+
+    df3 = pl.read_excel(
+        excel_file_path,
+        sheet_name="test4",
+        schema_overrides={"cardinality": pl.UInt16},
+        read_csv_options={
+            "dtypes": {
+                "rows_by_key": pl.Float32,
+                "iter_groups": pl.Float32,
+            },
+        },
+    ).drop_nulls()
+    assert df3.schema == {
+        "cardinality": pl.UInt16,
+        "rows_by_key": pl.Float32,
+        "iter_groups": pl.Float32,
+    }
+
+    with pytest.raises(ParameterCollisionError):
+        # cannot specify 'cardinality' in both schema_overrides and read_csv_options
+        pl.read_excel(
+            excel_file_path,
+            sheet_name="test4",
+            schema_overrides={"cardinality": pl.UInt16},
+            read_csv_options={"dtypes": {"cardinality": pl.Int32}},
+        )
+
+
 def test_unsupported_engine() -> None:
     with pytest.raises(NotImplementedError):
         pl.read_excel(None, engine="foo")  # type: ignore[call-overload]