m = expected_postal_format.match(postcode)

if not m:

osmfile = open(filename, 'r')

unexpected_postcodes = set()

for event, elem in ET.iterparse(osmfile, events=("start",)):

if elem.tag == 'node' or elem.tag == 'way':

for tag in elem.iter('tag'):

if is_postcode(tag):

check_postcode(unexpected_postcodes, tag.attrib['v'])

osmfile.close()