DEP: Protect some ExcelWriter attributes

doc/source/reference/io.rst

@@ -53,7 +53,6 @@ Excel
 
 .. autosummary::
    :toctree: api/
-   :template: autosummary/class_without_autosummary.rst
 
    ExcelWriter
 

doc/source/whatsnew/v1.5.0.rst

@@ -184,6 +184,43 @@ use ``series.loc[i:j]``.
 
 Slicing on a :class:`DataFrame` will not be affected.
 
+.. _whatsnew_150.deprecations.excel_writer_attributes:
+
+:class:`ExcelWriter` attributes
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+All attributes of :class:`ExcelWriter` were previously documented as not
+public. However some third party Excel engines documented accessing
+``ExcelWriter.book`` or ``ExcelWriter.sheets``, and users were utilizing these
+and possibly other attributes. Previously these attributes were not safe to use;
+e.g. modifications to ``ExcelWriter.book`` would not update ``ExcelWriter.sheets``
+and conversely. In order to support this, pandas has made some attributes public
+and improved their implementations so that they may now be safely used. (:issue:`45572`)
+
+The following attributes are now public and considered safe to access.
+
+ - ``book``
+ - ``check_extension``
+ - ``close``
+ - ``date_format``
+ - ``datetime_format``
+ - ``engine``
+ - ``if_sheet_exists``
+ - ``sheets``
+ - ``supported_extensions``
+
+The following attributes have been deprecated. They now raise a ``FutureWarning``
+when accessed and will removed in a future version. Users should be aware
+that their usage is considered unsafe, and can lead to unexpected results.
+
+ - ``cur_sheet``
+ - ``handles``
+ - ``path``
+ - ``save``
+ - ``write_cells``
+
+See the documentation of :class:`ExcelWriter` for further details.
+
 .. _whatsnew_150.deprecations.other:
 
 Other Deprecations

pandas/io/excel/_base.py

@@ -836,18 +836,8 @@ class ExcelWriter(metaclass=abc.ABCMeta):
 
             Use engine_kwargs instead.
 
-    Attributes
-    ----------
-    None
-
-    Methods
-    -------
-    None
-
     Notes
     -----
-    None of the methods and properties are considered public.
-
     For compatibility with CSV writers, ExcelWriter serializes lists
     and dicts to strings before writing.
 
@@ -1034,7 +1024,7 @@ def __new__(
         return object.__new__(cls)
 
     # declare external properties you can count on
-    path = None
+    _path = None
 
     @property
     @abc.abstractmethod
@@ -1054,7 +1044,16 @@ def sheets(self) -> dict[str, Any]:
         """Mapping of sheet names to sheet objects."""
         pass
 
+    @property
     @abc.abstractmethod
+    def book(self):
+        """
+        Book instance. Class type will depend on the engine used.
+
+        This attribute can be used to access engine-specific features.
+        """
+        pass
+
     def write_cells(
         self,
         cells,
@@ -1066,6 +1065,8 @@ def write_cells(
         """
         Write given formatted cells into Excel an excel sheet
 
+        .. deprecated:: 1.5.0
+
         Parameters
         ----------
         cells : generator
@@ -1077,12 +1078,47 @@ def write_cells(
         freeze_panes: int tuple of length 2
             contains the bottom-most row and right-most column to freeze
         """
-        pass
+        self._deprecate("write_cells")
+        return self._write_cells(cells, sheet_name, startrow, startcol, freeze_panes)
 
     @abc.abstractmethod
+    def _write_cells(
+        self,
+        cells,
+        sheet_name: str | None = None,
+        startrow: int = 0,
+        startcol: int = 0,
+        freeze_panes: tuple[int, int] | None = None,
+    ) -> None:
+        """
+        Write given formatted cells into Excel an excel sheet
+
+        Parameters
+        ----------
+        cells : generator
+            cell of formatted data to save to Excel sheet
+        sheet_name : str, default None
+            Name of Excel sheet, if None, then use self.cur_sheet
+        startrow : upper left cell row to dump data frame
+        startcol : upper left cell column to dump data frame
+        freeze_panes: int tuple of length 2
+            contains the bottom-most row and right-most column to freeze
+        """
+        pass
+
     def save(self) -> None:
         """
         Save workbook to disk.
+
+        .. deprecated:: 1.5.0
+        """
+        self._deprecate("save")
+        return self._save()
+
+    @abc.abstractmethod
+    def _save(self) -> None:
+        """
+        Save workbook to disk.
         """
         pass
 
@@ -1111,25 +1147,25 @@ def __init__(
         mode = mode.replace("a", "r+")
 
         # cast ExcelWriter to avoid adding 'if self.handles is not None'
-        self.handles = IOHandles(
+        self._handles = IOHandles(
             cast(IO[bytes], path), compression={"compression": None}
         )
         if not isinstance(path, ExcelWriter):
-            self.handles = get_handle(
+            self._handles = get_handle(
                 path, mode, storage_options=storage_options, is_text=False
             )
-        self.cur_sheet = None
+        self._cur_sheet = None
 
         if date_format is None:
-            self.date_format = "YYYY-MM-DD"
+            self._date_format = "YYYY-MM-DD"
         else:
-            self.date_format = date_format
+            self._date_format = date_format
         if datetime_format is None:
-            self.datetime_format = "YYYY-MM-DD HH:MM:SS"
+            self._datetime_format = "YYYY-MM-DD HH:MM:SS"
         else:
-            self.datetime_format = datetime_format
+            self._datetime_format = datetime_format
 
-        self.mode = mode
+        self._mode = mode
 
         if if_sheet_exists not in (None, "error", "new", "replace", "overlay"):
             raise ValueError(
@@ -1140,16 +1176,78 @@ def __init__(
             raise ValueError("if_sheet_exists is only valid in append mode (mode='a')")
         if if_sheet_exists is None:
             if_sheet_exists = "error"
-        self.if_sheet_exists = if_sheet_exists
+        self._if_sheet_exists = if_sheet_exists
+
+    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 "
+            "results and will be removed in a future version",
+            FutureWarning,
+            stacklevel=find_stack_level(),
+        )
+
+    @property
+    def date_format(self) -> str:
+        """
+        Format string for dates written into Excel files (e.g. ‘YYYY-MM-DD’).
+        """
+        return self._date_format
+
+    @property
+    def datetime_format(self) -> str:
+        """
+        Format string for dates written into Excel files (e.g. ‘YYYY-MM-DD’).
+        """
+        return self._datetime_format
+
+    @property
+    def if_sheet_exists(self) -> str:
+        """
+        How to behave when writing to a sheet that already exists in append mode.
+        """
+        return self._if_sheet_exists
+
+    @property
+    def cur_sheet(self):
+        """
+        Current sheet for writing.
+
+        .. deprecated:: 1.5.0
+        """
+        self._deprecate("cur_sheet")
+        return self._cur_sheet
+
+    @property
+    def handles(self):
+        """
+        Handles to Excel sheets.
+
+        .. deprecated:: 1.5.0
+        """
+        self._deprecate("handles")
+        return self._handles
+
+    @property
+    def path(self):
+        """
+        Path to Excel file.
+
+        .. deprecated:: 1.5.0
+        """
+        self._deprecate("path")
+        return self._path
 
     def __fspath__(self):
-        return getattr(self.handles.handle, "name", "")
+        return getattr(self._handles.handle, "name", "")
 
     def _get_sheet_name(self, sheet_name: str | None) -> str:
         if sheet_name is None:
-            sheet_name = self.cur_sheet
+            sheet_name = self._cur_sheet
         if sheet_name is None:  # pragma: no cover
-            raise ValueError("Must pass explicit sheet_name or set cur_sheet property")
+            raise ValueError("Must pass explicit sheet_name or set _cur_sheet property")
         return sheet_name
 
     def _value_with_fmt(self, val) -> tuple[object, str | None]:
@@ -1175,9 +1273,9 @@ def _value_with_fmt(self, val) -> tuple[object, str | None]:
         elif is_bool(val):
             val = bool(val)
         elif isinstance(val, datetime.datetime):
-            fmt = self.datetime_format
+            fmt = self._datetime_format
         elif isinstance(val, datetime.date):
-            fmt = self.date_format
+            fmt = self._date_format
         elif isinstance(val, datetime.timedelta):
             val = val.total_seconds() / 86400
             fmt = "0"
@@ -1213,8 +1311,8 @@ def __exit__(self, exc_type, exc_value, traceback):
 
     def close(self) -> None:
         """synonym for save, to make it more file-like"""
-        self.save()
-        self.handles.close()
+        self._save()
+        self._handles.close()
 
 
 XLS_SIGNATURES = (

pandas/io/excel/_odswriter.py

@@ -55,9 +55,18 @@ def __init__(
 
         engine_kwargs = combine_kwargs(engine_kwargs, kwargs)
 
-        self.book = OpenDocumentSpreadsheet(**engine_kwargs)
+        self._book = OpenDocumentSpreadsheet(**engine_kwargs)
         self._style_dict: dict[str, str] = {}
 
+    @property
+    def book(self):
+        """
+        Book instance of class odf.opendocument.OpenDocumentSpreadsheet.
+
+        This attribute can be used to access engine-specific features.
+        """
+        return self._book
+
     @property
     def sheets(self) -> dict[str, Any]:
         """Mapping of sheet names to sheet objects."""
@@ -69,15 +78,15 @@ def sheets(self) -> dict[str, Any]:
         }
         return result
 
-    def save(self) -> None:
+    def _save(self) -> None:
         """
         Save workbook to disk.
         """
         for sheet in self.sheets.values():
             self.book.spreadsheet.addElement(sheet)
-        self.book.save(self.handles.handle)
+        self.book.save(self._handles.handle)
 
-    def write_cells(
+    def _write_cells(
         self,
         cells: list[ExcelCell],
         sheet_name: str | None = None,