mt940_to_ynab.py

import csv
from datetime import datetime
import sys

mt940_reader = csv.DictReader(sys.stdin, delimiter=';')
ynab_writer = csv.DictWriter(sys.stdout, fieldnames=('Date', 'Payee', 'Category', 'Memo', 'Outflow', 'Inflow'))
ynab_writer.writeheader()

for mt940_row in mt940_reader:
    valuation_date = datetime.strptime(mt940_row['Valutadatum'], '%d.%m.%y')
    value = float(mt940_row['Betrag'].replace(',', '.'))

    ynab_row = {
        'Date': valuation_date.strftime('%d/%m/%y'),
        'Payee': mt940_row['Beguenstigter/Zahlungspflichtiger'],
        'Memo': mt940_row['Buchungstext'],
    }

    if value > 0:
        ynab_row['Inflow'] = value
    else:
        ynab_row['Outflow'] = abs(value)

    ynab_writer.writerow(ynab_row)