Backport PR #48943 on branch 1.5.x (REGR: ExcelWriter.book not settable)

doc/source/whatsnew/v1.5.1.rst

@@ -84,6 +84,7 @@ Fixed regressions
 - Fixed Regression in :meth:`DataFrameGroupBy.apply` when user defined function is called on an empty dataframe (:issue:`47985`)
 - Fixed regression in :meth:`DataFrame.apply` when passing non-zero ``axis`` via keyword argument (:issue:`48656`)
 - Fixed regression in :meth:`Series.groupby` and :meth:`DataFrame.groupby` when the grouper is a nullable data type (e.g. :class:`Int64`) or a PyArrow-backed string array, contains null values, and ``dropna=False`` (:issue:`48794`)
+- Fixed regression in :class:`ExcelWriter` where the ``book`` attribute could no longer be set; however setting this attribute is now deprecated and this ability will be removed in a future version of pandas (:issue:`48780`)
 
 .. ---------------------------------------------------------------------------
 

pandas/io/excel/_base.py

@@ -1192,7 +1192,9 @@ def sheets(self) -> dict[str, Any]:
         """Mapping of sheet names to sheet objects."""
         pass
 
-    @property
+    # mypy doesn't handle abstract setters prior to 0.981
+    # https://github.com/python/mypy/issues/4165
+    @property  # type: ignore[misc]
     @abc.abstractmethod
     def book(self):
         """
@@ -1202,6 +1204,16 @@ def book(self):
         """
         pass
 
+    # mypy doesn't handle abstract setters prior to 0.981
+    # https://github.com/python/mypy/issues/4165
+    @book.setter  # type: ignore[misc]
+    @abc.abstractmethod
+    def book(self, other) -> None:
+        """
+        Set book instance. Class type will depend on the engine used.
+        """
+        pass
+
     def write_cells(
         self,
         cells,
@@ -1331,12 +1343,24 @@ def _deprecate(self, attr: str):
         Deprecate attribute or method for ExcelWriter.
         """
         warnings.warn(
-            f"{attr} is not part of the public API, usage can give in unexpected "
+            f"{attr} is not part of the public API, usage can give unexpected "
             "results and will be removed in a future version",
             FutureWarning,
             stacklevel=find_stack_level(inspect.currentframe()),
         )
 
+    def _deprecate_set_book(self) -> None:
+        """
+        Deprecate setting the book attribute - GH#48780.
+        """
+        warnings.warn(
+            "Setting the `book` attribute is not part of the public API, "
+            "usage can give unexpected or corrupted results and will be "
+            "removed in a future version",
+            FutureWarning,
+            stacklevel=find_stack_level(inspect.currentframe()),
+        )
+
     @property
     def date_format(self) -> str:
         """

pandas/io/excel/_odswriter.py

@@ -24,6 +24,8 @@
 )
 
 if TYPE_CHECKING:
+    from odf.opendocument import OpenDocumentSpreadsheet
+
     from pandas.io.formats.excel import ExcelCell
 
 
@@ -70,6 +72,14 @@ def book(self):
         """
         return self._book
 
+    @book.setter
+    def book(self, other: OpenDocumentSpreadsheet) -> None:
+        """
+        Set book instance. Class type will depend on the engine used.
+        """
+        self._deprecate_set_book()
+        self._book = other
+
     @property
     def sheets(self) -> dict[str, Any]:
         """Mapping of sheet names to sheet objects."""

pandas/io/excel/_openpyxl.py

@@ -88,6 +88,14 @@ def book(self) -> Workbook:
         """
         return self._book
 
+    @book.setter
+    def book(self, other: Workbook) -> None:
+        """
+        Set book instance. Class type will depend on the engine used.
+        """
+        self._deprecate_set_book()
+        self._book = other
+
     @property
     def sheets(self) -> dict[str, Any]:
         """Mapping of sheet names to sheet objects."""

pandas/io/excel/_xlsxwriter.py

@@ -1,6 +1,9 @@
 from __future__ import annotations
 
-from typing import Any
+from typing import (
+    TYPE_CHECKING,
+    Any,
+)
 
 import pandas._libs.json as json
 from pandas._typing import (
@@ -15,6 +18,9 @@
     validate_freeze_panes,
 )
 
+if TYPE_CHECKING:
+    from xlsxwriter import Workbook
+
 
 class _XlsxStyler:
     # Map from openpyxl-oriented styles to flatter xlsxwriter representation
@@ -218,6 +224,14 @@ def book(self):
         """
         return self._book
 
+    @book.setter
+    def book(self, other: Workbook) -> None:
+        """
+        Set book instance. Class type will depend on the engine used.
+        """
+        self._deprecate_set_book()
+        self._book = other
+
     @property
     def sheets(self) -> dict[str, Any]:
         result = self.book.sheetnames

pandas/io/excel/_xlwt.py

@@ -21,7 +21,10 @@
 )
 
 if TYPE_CHECKING:
-    from xlwt import XFStyle
+    from xlwt import (
+        Workbook,
+        XFStyle,
+    )
 
 
 class XlwtWriter(ExcelWriter):
@@ -64,14 +67,22 @@ def __init__(
         self._fm_date = xlwt.easyxf(num_format_str=self._date_format)
 
     @property
-    def book(self):
+    def book(self) -> Workbook:
         """
         Book instance of class xlwt.Workbook.
 
         This attribute can be used to access engine-specific features.
         """
         return self._book
 
+    @book.setter
+    def book(self, other: Workbook) -> None:
+        """
+        Set book instance. Class type will depend on the engine used.
+        """
+        self._deprecate_set_book()
+        self._book = other
+
     @property
     def sheets(self) -> dict[str, Any]:
         """Mapping of sheet names to sheet objects."""

pandas/tests/io/excel/test_writers.py

@@ -1301,6 +1301,17 @@ def test_deprecated_method(self, engine, ext, attr, args):
                 with tm.assert_produces_warning(FutureWarning, match=msg):
                     getattr(writer, attr)(*args)
 
+    def test_deprecated_book_setter(self, engine, ext):
+        # GH#48780
+        with tm.ensure_clean(ext) as path:
+            with ExcelWriter(path) as writer:
+                msg = "Setting the `book` attribute is not part of the public API"
+                # Some engines raise if nothing is written
+                DataFrame().to_excel(writer)
+                book = writer.book
+                with tm.assert_produces_warning(FutureWarning, match=msg):
+                    writer.book = book
+
 
 class TestExcelWriterEngineTests:
     @pytest.mark.parametrize(