REGR: do not try to infer the excel type from a workbook object

doc/source/whatsnew/v1.2.2.rst

@@ -21,6 +21,7 @@ Fixed regressions
 - Fixed regression in :meth:`~DataFrame.to_pickle` failing to create bz2/xz compressed pickle files with ``protocol=5`` (:issue:`39002`)
 - Fixed regression in :func:`pandas.testing.assert_series_equal` and :func:`pandas.testing.assert_frame_equal` always raising ``AssertionError`` when comparing extension dtypes (:issue:`39410`)
 - Fixed regression in :meth:`~DataFrame.to_csv` opening ``codecs.StreamWriter`` in binary mode instead of in text mode and ignoring user-provided ``mode`` (:issue:`39247`)
+- Fixed regression in :func:`read_excel` that caused it to raise a ``ValueError`` when mistakenly treating a workbook object as a file handle (:issue:`39528`)
 -
 
 .. ---------------------------------------------------------------------------

pandas/io/excel/_base.py

@@ -1071,7 +1071,7 @@ def __init__(
 
         if xlrd_version is not None and isinstance(path_or_buffer, xlrd.Book):
             ext = "xls"
-        else:
+        elif engine in (None, "xlrd") and True:
             ext = inspect_excel_format(
                 content_or_path=path_or_buffer, storage_options=storage_options
             )

pandas/tests/io/excel/test_openpyxl.py

@@ -116,3 +116,27 @@ def test_to_excel_with_openpyxl_engine(ext):
         ).highlight_max()
 
         styled.to_excel(filename, engine="openpyxl")
+
+
+@pytest.mark.parametrize("engine", (None, "openpyxl"))
+def test_read_excel_workbook(engine, ext):
+    # GH 39528
+    openpyxl = pytest.importorskip("openpyxl")
+    expected = tm.makeDataFrame()
+    message = "Invalid file path or buffer object type"
+
+    with tm.ensure_clean(ext) as filename:
+        expected.to_excel(filename)
+        workbook = openpyxl.load_workbook(filename)
+        if engine is None:
+            # should raise
+            try:
+                with pytest.raises(ValueError, match=message):
+                    df = pd.read_excel(workbook, engine=engine)
+            finally:
+                workbook.close()
+        else:
+            # should work
+            df = pd.read_excel(workbook, engine=engine, index_col=0)
+            workbook.close()
+            tm.assert_frame_equal(expected, df)