help with changing values in an excel sheet and saving to a new file

[snippsat]

Most likely you have a empty cell in transactions.xlsx.
Check cell after value 7.155.
To make the error.

>>> cell = None
>>> cell * 0.9
Traceback (most recent call last):
  File "<interactive input>", line 1, in <module>
TypeError: unsupported operand type(s) for *: 'NoneType' and 'float'

You can fix file bye add a value,or bypass(pass) the error as shown under.

import openpyxl as xl

wb = xl.load_workbook('transactions.xlsx')
sheet = wb['Sheet1']
cell = sheet['a1']
cell = sheet.cell(1, 1)
print(cell.value)

for row in range(2, sheet.max_row + 1):
    cell = sheet.cell(row, 3)
    try:
        corrected_price = cell.value * 0.9
    except TypeError:
        pass
    corrected_price_cell = sheet.cell(row, 4)
    corrected_price_cell.value = corrected_price
    print(corrected_price)

wb.save('transactions 2.xlsx')