CLN: Moved freeze_panes validation to io/excel.py (#15160)

follow up to #15160

Author: Jeff Carey <jeff.carey@gmail.com>

Closes #15592 from jeffcarey/enh-15160-touchup2 and squashes the following commits:

81cb86f [Jeff Carey] Cleaned up freeze_panes validation code
a802fc7 [Jeff Carey] Moved freeze_panes validation to io/excel.py

pandas/core/frame.py

@@ -1431,24 +1431,12 @@ def to_excel(self, excel_writer, sheet_name='Sheet1', na_rep='',
                                        inf_rep=inf_rep)
 
         formatted_cells = formatter.get_formatted_cells()
-        freeze_panes = self._validate_freeze_panes(freeze_panes)
         excel_writer.write_cells(formatted_cells, sheet_name,
                                  startrow=startrow, startcol=startcol,
                                  freeze_panes=freeze_panes)
         if need_save:
             excel_writer.save()
 
-    def _validate_freeze_panes(self, freeze_panes):
-        if freeze_panes is not None:
-            if (
-                len(freeze_panes) == 2 and
-                all(isinstance(item, int) for item in freeze_panes)
-            ):
-                return freeze_panes
-
-                raise ValueError("freeze_panes must be of form (row, column)"
-                                 " where row and column are integers")
-
     def to_stata(self, fname, convert_dates=None, write_index=True,
                  encoding="latin-1", byteorder=None, time_stamp=None,
                  data_label=None, variable_labels=None):

pandas/io/excel.py

@@ -543,6 +543,22 @@ def __exit__(self, exc_type, exc_value, traceback):
         self.close()
 
 
+def _validate_freeze_panes(freeze_panes):
+    if freeze_panes is not None:
+        if (
+            len(freeze_panes) == 2 and
+            all(isinstance(item, int) for item in freeze_panes)
+        ):
+            return True
+
+        raise ValueError("freeze_panes must be of form (row, column)"
+                         " where row and column are integers")
+
+    # freeze_panes wasn't specified, return False so it won't be applied
+    # to output sheet
+    return False
+
+
 def _trim_excel_header(row):
     # trim header row so auto-index inference works
     # xlrd uses '' , openpyxl None
@@ -1330,7 +1346,7 @@ def write_cells(self, cells, sheet_name=None, startrow=0, startcol=0,
             wks.title = sheet_name
             self.sheets[sheet_name] = wks
 
-        if freeze_panes is not None:
+        if _validate_freeze_panes(freeze_panes):
             wks.freeze_panes = wks.cell(row=freeze_panes[0] + 1,
                                         column=freeze_panes[1] + 1)
 
@@ -1418,7 +1434,7 @@ def write_cells(self, cells, sheet_name=None, startrow=0, startcol=0,
             wks = self.book.add_sheet(sheet_name)
             self.sheets[sheet_name] = wks
 
-        if freeze_panes is not None:
+        if _validate_freeze_panes(freeze_panes):
             wks.set_panes_frozen(True)
             wks.set_horz_split_pos(freeze_panes[0])
             wks.set_vert_split_pos(freeze_panes[1])
@@ -1550,7 +1566,7 @@ def write_cells(self, cells, sheet_name=None, startrow=0, startcol=0,
 
         style_dict = {}
 
-        if freeze_panes is not None:
+        if _validate_freeze_panes(freeze_panes):
             wks.freeze_panes(*(freeze_panes))
 
         for cell in cells: