Using Openpyxl To Increment A Date In Excel

Question

I'm trying to increment a date using openpyxl. Here's some example code:

import openpyxl
import os
import datetime

os.chdir("C:\\Personal\\Rentals\\xxxx")

wb = openpyxl.load_workbook(filename = 'Income_Receipts.xlsx', read_only=False)
sheet = wb['Sheet1']
cellreference = "B" +str(6)
cell = sheet[cellreference]

def LastRowNumber():
    global sheet, cellreference, cell
    i = 4
    BlankRowNumber = 0
    while BlankRowNumber == 0:
        i = i + 1
        cellreference = "B" + str(i)
        cell = sheet[cellreference]
        if cell.value == None:
            BlankRowNumber = i
    return i

def FormatDatesToNumbers(RowNumber):
    global sheet, cellreference, cell, wb
    #if sheet["B" + str(RowNumber)].value == "Airbnb":
    sheet["I" + str(RowNumber)].number_format = "######.0"
    sheet["F" + str(RowNumber)].number_format = "######.0"
    wb.save('Income_Receipts.xlsx')


def AirbnbDueDates(RowNumber):
    global sheet, wb
    if sheet.cell(row = RowNumber, column = 2).value =="Airbnb":
        DateAsFloat = sheet["F" + str(RowNumber)].value + 5
        sheet["I" + str(RowNumber)] = DateAsFloat + 5
        wb.save('Income_Receipts.xlsx')

LastRowToProcess = LastRowNumber() - 1

i = 4

while i <= LastRowToProcess:
    i = i + 1
    FormatDatesToNumbers(i)

i = 4

while i <= LastRowToProcess:
    i = i + 1
    AirbnbDueDates(i)

wb.save('Income_Receipts.xlsx')

Please excuse the code if its a little untidy - I keep playing around trying to get around the issue which is - I get the following error message: TypeError: unsupported operand type(s) for +: 'datetime.datetime' and 'int'

The issue is I am trying to increment a given date by 5 days for example - but I can't mix datetime.datetime and ints. I've tried typecasting the datetime to an int or a float, but that doesn't work...

If I manually open the excel sheet and change the data type to an integer (as I try to do in my code above) then my code works fine. However if the relevant cells are formatted as a date I get the error.

I thought saving the worksheet after the change in formatting would sort the issue, but unfortunately not...

Any pointers much appreciated,

Thanks

Rob