def get_sid(self):
        """Returns a valid SID"""
        base_url = u'%s/login_sid.lua' % self.__fritz_url
        get_challenge = None
        try:
            get_challenge = urllib2.urlopen(base_url).read().decode('ascii')
        except urllib2.HTTPError as exception:
            print('HTTPError = ' + str(exception.code))
        except urllib2.URLError as  exception:
            print('URLError = ' + str(exception.reason))
        except Exception as exception:
            print('generic exception: ' + str(exception))
            raise


        challenge = get_challenge.split(
            '<Challenge>')[1].split('</Challenge>')[0]
        challenge_b = (
            challenge + '-' + self.__password).encode().decode('iso-8859-1').encode('utf-16le')

        md5hash = hashlib.md5()
        md5hash.update(challenge_b)

        response_b = challenge + '-' + md5hash.hexdigest().lower()
        get_sid = urllib2.urlopen('%s?%sresponse=%s' % (base_url, self.__username_query, response_b)).read().decode('utf-8')
        self.sid = get_sid.split('<SID>')[1].split('</SID>')[0]
Returns a valid SID