Close the workbook in get_xlsx_sheet_info (#1051)

CHANGELOG.md

@@ -19,7 +19,9 @@ All notable changes to Fair Code are documented here, newest first.
 
 ## [Unreleased]
 
-Nothing yet. Changes made after 2.3.0 are listed here until the next release.
+### Fixed
+
+- `get_xlsx_sheet_info` now closes the workbook it opens to list sheet names, rather than leaking the file handle. The unclosed handle raised a `ResourceWarning` on garbage collection and, on Windows, kept the `.xlsx` locked against deletion or overwrite ([#1051](https://github.com/yakew7/Fair-Code/issues/1051)).
 
 ## [2.3.0] - 17 Oct 2026
 

faircode/loaders_extra.py

@@ -172,12 +172,13 @@ def get_xlsx_sheet_info(path: str) -> tuple[str, list[str]] | None:
     if Path(path).suffix.lower() != ".xlsx":
         return None
     try:
-        book = pd.ExcelFile(path)
+        with pd.ExcelFile(path) as book:
+            sheet_names = book.sheet_names
     except Exception:
         return None
-    if not book.sheet_names:
+    if not sheet_names:
         return None
-    return book.sheet_names[0], book.sheet_names[1:]
+    return sheet_names[0], sheet_names[1:]
 
 
 # Binary table formats that never decode as text, so an explicit text encoding

tests/test_loaders.py

@@ -3,8 +3,10 @@
 Run from the repo root:  pytest tests/ -q
 """
 
+import gc
 import importlib.util
 import json
+import warnings
 
 import pandas as pd
 import pytest
@@ -204,6 +206,30 @@ def test_get_xlsx_sheet_info_returns_none_for_a_corrupt_xlsx_file(tmp_path):
     assert get_xlsx_sheet_info(str(path)) is None
 
 
+@requires_openpyxl
+def test_get_xlsx_sheet_info_closes_the_workbook(tmp_path):
+    # Listing sheet names must not leak the workbook's file handle: an unclosed
+    # handle raises a ResourceWarning on garbage collection and, on Windows,
+    # keeps the file locked against deletion or overwrite (#1051).
+    path = tmp_path / "multi.xlsx"
+    with pd.ExcelWriter(path) as writer:
+        pd.DataFrame(ROWS).to_excel(writer, sheet_name="First", index=False)
+        pd.DataFrame(ROWS).to_excel(writer, sheet_name="Second", index=False)
+
+    with warnings.catch_warnings(record=True) as caught:
+        warnings.simplefilter("always")
+        info = get_xlsx_sheet_info(str(path))
+        gc.collect()
+
+    assert info == ("First", ["Second"])
+    unclosed = [
+        w
+        for w in caught
+        if issubclass(w.category, ResourceWarning) and "unclosed" in str(w.message)
+    ]
+    assert not unclosed, f"workbook left open: {[str(w.message) for w in unclosed]}"
+
+
 def test_read_table_unknown_extension_sniffs_tabs(tmp_path):
     path = tmp_path / "data.txt"
     _write_csv(path, sep="\t")