feat(python): Allow loading data from multiple Excel/ODS workbooks an…

…d worksheets

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

@@ -3,6 +3,7 @@
 import os
 import re
 import warnings
+from collections import defaultdict
 from collections.abc import Sequence
 from datetime import time
 from glob import glob
@@ -71,6 +72,31 @@ def _standardize_duplicates(s: str) -> str:
     return re.sub(r"_duplicated_(\d+)", repl=r"\1", string=s)
 
 
+def _unpack_sheet_results(
+    frames: list[pl.DataFrame] | list[dict[str, pl.DataFrame]],
+    *,
+    read_multiple_workbooks: bool,
+) -> Any:
+    if not frames:
+        msg = "no data found in the given workbook(s) and sheet(s)"
+        raise NoDataError(msg)
+
+    if not read_multiple_workbooks:
+        # one sheet from one workbook
+        return frames[0]
+
+    if isinstance(frames[0], pl.DataFrame):
+        # one sheet from multiple workbooks
+        return concat(frames, how="vertical_relaxed")  # type: ignore[type-var]
+    else:
+        # multiple sheets from multiple workbooks
+        sheet_frames = defaultdict(list)
+        for res in frames:
+            for sheet, df in res.items():  # type: ignore[union-attr]
+                sheet_frames[sheet].append(df)
+        return {k: concat(v, how="vertical_relaxed") for k, v in sheet_frames.items()}
+
+
 @overload
 def read_excel(
     source: FileSource,
@@ -338,7 +364,7 @@ def read_excel(
     ... )  # doctest: +SKIP
     """
     sources, read_multiple_workbooks = _sources(source)
-    frames = [
+    frames: list[pl.DataFrame] | list[dict[str, pl.DataFrame]] = [  # type: ignore[assignment]
         _read_spreadsheet(
             src,
             sheet_id=sheet_id,
@@ -357,9 +383,10 @@ def read_excel(
         )
         for src in sources
     ]
-    if read_multiple_workbooks:
-        return concat(frames, how="vertical_relaxed")  # type: ignore[type-var]
-    return frames[0]
+    return _unpack_sheet_results(
+        frames=frames,
+        read_multiple_workbooks=read_multiple_workbooks,
+    )
 
 
 @overload
@@ -540,7 +567,7 @@ def read_ods(
     ... )  # doctest: +SKIP
     """
     sources, read_multiple_workbooks = _sources(source)
-    frames = [
+    frames: list[pl.DataFrame] | list[dict[str, pl.DataFrame]] = [  # type: ignore[assignment]
         _read_spreadsheet(
             src,
             sheet_id=sheet_id,
@@ -559,9 +586,10 @@ def read_ods(
         )
         for src in sources
     ]
-    if read_multiple_workbooks:
-        return concat(frames, how="vertical_relaxed")  # type: ignore[type-var]
-    return frames[0]
+    return _unpack_sheet_results(
+        frames=frames,
+        read_multiple_workbooks=read_multiple_workbooks,
+    )
 
 
 def _read_spreadsheet(
@@ -605,10 +633,6 @@ def _read_spreadsheet(
         sheet_names, return_multiple_sheets = _get_sheet_names(
             sheet_id, sheet_name, worksheets
         )
-        if read_multiple_workbooks and return_multiple_sheets:
-            msg = "cannot return multiple sheets from multiple workbooks"
-            raise ValueError(msg)
-
         parsed_sheets = {
             name: reader_fn(
                 parser=parser,

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

@@ -184,13 +184,14 @@ def test_read_excel_multiple_worksheets(
     ],
 )
 def test_read_excel_multiple_workbooks(
-    read_spreadsheet: Callable[..., pl.DataFrame],
+    read_spreadsheet: Callable[..., Any],
     source: str,
     params: dict[str, str],
     request: pytest.FixtureRequest,
 ) -> None:
     spreadsheet_path = request.getfixturevalue(source)
 
+    # multiple workbooks, single worksheet
     df = read_spreadsheet(
         [
             spreadsheet_path,
@@ -206,6 +207,29 @@ def test_read_excel_multiple_workbooks(
     )
     assert_frame_equal(df, expected)
 
+    # multiple workbooks, multiple worksheets
+    res = read_spreadsheet(
+        [
+            spreadsheet_path,
+            spreadsheet_path,
+            spreadsheet_path,
+        ],
+        sheet_id=None,
+        sheet_name=["test1", "test2"],
+        **params,
+    )
+    expected_frames = {
+        "test1": pl.DataFrame(
+            {"hello": ["Row 1", "Row 2", "Row 1", "Row 2", "Row 1", "Row 2"]}
+        ),
+        "test2": pl.DataFrame(
+            {"world": ["Row 3", "Row 4", "Row 3", "Row 4", "Row 3", "Row 4"]}
+        ),
+    }
+    assert sorted(res) == sorted(expected_frames)
+    assert_frame_equal(res["test1"], expected_frames["test1"])
+    assert_frame_equal(res["test2"], expected_frames["test2"])
+
 
 @pytest.mark.parametrize(
     ("read_spreadsheet", "source", "params"),