import openpyxl as xl
from openpyxl.chart import BarChart, Reference


def process_workbook(filename):
    # accessing a workbook
    workbook = xl.load_workbook(filename)
    # accessing a sheet in the workbook
    sheet = workbook["Sheet1"]

    for row in range(2, sheet.max_row + 1):
        cell = sheet.cell(row, 3)
        corrected_price = cell.value * 0.9
        corrected_price_cell = sheet.cell(row, 4)
        corrected_price_cell.value = round(corrected_price, 2)

    values = Reference(sheet, min_row=2, max_row=sheet.max_row, min_col=4, max_col=4)

    chart = BarChart()
    chart.add_data(values)
    sheet.add_chart(chart, "b10")

    workbook.save(filename)

