openpyxl ValueError formatting new rows of data - python-3.x

Question

The following code works great the first time I run it (when it creates a new spreadsheet).
When I try to run it again (update existing sheet) to add more data (additional rows) I get the following error
Traceback (most recent call last):
File "C:/PythonPrograms/Workout Program/test_excel_format.py", line 35, in
cell.style = wdata
File "C:\Users\Mark\AppData\Local\Programs\Python\Python37\lib\site-packages\openpyxl\styles\named_styles.py", line 193, in append
raise ValueError("""Style {0} exists already""".format(style.name))
ValueError: Style wdata exists already
from openpyxl import Workbook
from openpyxl.styles import PatternFill
from openpyxl import load_workbook
from openpyxl.styles import Font, Color, Alignment, Border, Side, colors
from openpyxl.styles import NamedStyle
from datetime import date
from os import path
filename = "format_wb_test.xlsx"
if path.exists(filename):
workbook = load_workbook(filename)
else:
workbook = Workbook()
sheet = workbook.active
tdate = date.today()
data = [tdate, "Data 1", "Data 2", "Data 3"]
wdata = NamedStyle(name="wdata")
wdata.font = Font(bold=True)
wdata.alignment = Alignment(horizontal="center", vertical="center")
for x in range(1, 3):
sheet.append(data) # appends the data to the first empty row.
print("current row: ", sheet._current_row)
ucell = "A" + str(sheet._current_row)
wdata_row = sheet[sheet._current_row]
for cell in wdata_row:
cell.style = wdata
sheet[ucell] = tdate
workbook.save(filename=filename)
I want to be able to add new rows of formatted data esch time I run this code.

Answer 1

I don't see any way to use a NamedStyle to update the format for rows added to an existing
workbook/sheet. If you define the NamedStyle you get the "Already Exists" error. If you don't then you get an error that the "NamedStyle is not defined". The doc states pretty much verbatim what Charlie Clark said in his comment above, "Styles registered automatically on their first use and can then be referenced by name." It does not elaborate or show examples of how to use an existing NamedStyle. Given this I gave up trying to use a NamedStyle and updated the code as follows to make it work. If there is a way to do this with NamedStyle I'd love to see it.
Here's the updated code.
from openpyxl import Workbook
from openpyxl.styles import PatternFill
from openpyxl import load_workbook
from openpyxl.styles import Font, Color, Alignment, Border, Side, colors
from openpyxl.styles import NamedStyle
from datetime import date
from os import path
filename = "format_wb_test.xlsx"
if path.exists(filename):
workbook = load_workbook(filename)
else:
workbook = Workbook()
sheet = workbook.active
tdate = date.today()
data = [tdate, "Data 1", "Data 2", "Data 3"]
# wdata = NamedStyle(name="wdata")
# wdata.font = Font(bold=True)
# wdata.alignment = Alignment(horizontal="center", vertical="center")
for x in range(1, 3):
sheet.append(data) # appends the data to the first empty row.
print("current row: ", sheet._current_row)
ucell = "A" + str(sheet._current_row)
wdata_row = sheet[sheet._current_row]
for cell in wdata_row:
#cell.style = wdata
sheet[str(cell.coordinate)].font = Font(bold=True)
sheet[str(cell.coordinate)].alignment = Alignment \
(horizontal="center", vertical="center")
sheet[ucell] = tdate
workbook.save(filename=filename)