Lee información de facturas en formato cfdi 3.3 y suma los impuestos

sum.py

from xml.dom.minidom import parse
import os
import sys


def main():
    if len(sys.argv) < 2:
        exit('Usage: sum.py folder-with-xmls')

    dirname = sys.argv[1]

    if not os.path.isdir(dirname):
        exit('argument must be a directory')

    total = 0.0

    for filename in os.listdir(dirname):
        if not filename.endswith('.xml'):
            continue

        dom = parse(os.path.join(dirname, filename))

        print(dom.getElementsByTagName('cfdi:Comprobante')[0].getAttribute('Fecha'))

        for item in dom.getElementsByTagName('cfdi:Concepto'):
            print('\t{}…: {}x{}'.format(
                item.getAttribute('Descripcion')[:15],
                item.getAttribute('ValorUnitario'),
                item.getAttribute('Cantidad'),
            ))

            for tax in item.getElementsByTagName('cfdi:Traslado'):
                amount = float(tax.getAttribute('Importe'))

                print('\t\t{}'.format(amount))
                total += amount

    print(total)


if __name__ == '__main__':
    main()