Musterlösung mit Erklärung

import csv
from openpyxl import Workbook
from openpyxl.styles import Font

# 1: einlesen
with open('verkaeufe.csv', newline='', encoding='utf-8-sig') as f:
    zeilen = list(csv.DictReader(f, delimiter=';'))

for z in zeilen:
    z['menge'] = int(z['menge'])
    z['preis'] = float(z['preis'])
    z['umsatz'] = z['menge'] * z['preis']

# 2: pro Kunde summieren
pro_kunde = {}
for z in zeilen:
    pro_kunde[z['kunde']] = pro_kunde.get(z['kunde'], 0) + z['umsatz']

# 3: Excel schreiben
wb = Workbook()

ws1 = wb.active
ws1.title = 'Details'
ws1.append(['Kunde', 'Artikel', 'Menge', 'Preis', 'Umsatz'])
for z in zeilen:
    ws1.append([z['kunde'], z['artikel'], z['menge'], z['preis'], z['umsatz']])
letzte = ws1.max_row
ws1.append(['', '', '', 'Summe', f'=SUM(E2:E{letzte})'])

ws2 = wb.create_sheet('Pro Kunde')
ws2.append(['Kunde', 'Umsatz'])
for kunde, summe in sorted(pro_kunde.items(), key=lambda p: p[1], reverse=True):
    ws2.append([kunde, summe])

# 4: formatieren
for ws in (ws1, ws2):
    for zelle in ws[1]:
        zelle.font = Font(bold=True)
    ws.column_dimensions['A'].width = 16
for zeile in ws1.iter_rows(min_row=2, min_col=4, max_col=5):
    for zelle in zeile:
        zelle.number_format = '0.00'
for zeile in ws2.iter_rows(min_row=2, min_col=2, max_col=2):
    zeile[0].number_format = '0.00'

wb.save('auswertung.xlsx')