See
        http://web.archive.org/web/20090930140939/http://www.govtalk.gov.uk/gdsc/html/noframes/PostCode-2-1-Release.htm

def postcode(self):
        """
        See
        http://web.archive.org/web/20090930140939/http://www.govtalk.gov.uk/gdsc/html/noframes/PostCode-2-1-Release.htm
        """
        postcode = ''
        pattern = self.random_element(self.postcode_formats)
        for placeholder in pattern:
            postcode += self.random_element(self._postcode_sets[placeholder])
        return postcode