Find Invoices to get a Payment reminder

gistfile1.py

def get_invoices(datum):
    """Returns a dict if invoices generated before `datum` and unpayed."""
    # Create your consumer with the proper key/secret.
    consumer = oauth.Consumer(key=CONSUMER_KEY, secret=CONSUMER_SECRET)
    client = oauth.Client(consumer, token=oauth.Token(key=CONSUMER_KEY, secret=CONSUMER_SECRET))
    client.set_signature_method(XeroOAuthSignatureMethod_RSA_SHA1())
    urlbase = 'https://api.xero.com/api.xro/2.0/Invoices'
    datum = datum.strftime('%Y-%m-%dT00:00:00')
    query = 'Date<=DateTime.Parse("%s")&&Status=="AUTHORISED"&&AmountPaid==0' % datum
    url = "%s?%s&order=DueDate" % (urlbase, urllib.urlencode({'where': query}))
    resp, content = client.request(url, "GET")
    xml = ET.fromstring(content)
    invoices = {}
    for i in xml.getiterator('Invoice'):
        ref = i.findtext('Reference')
        if ref and (ref.startswith('WL') or ref.startswith('SF')):
            invoice = {}
            for attr in '''Reference Date DueDate Status LineAmountTypes SubTotal TotalTax Total UpdatedDateUTC
                           CurrencyCode InvoiceID InvoiceNumber AmountDue AmountPaid'''.split():
                invoice[attr] = i.find(attr).text.strip()
            invoices[ref.strip()] = invoice
    return invoices