@classmethod
def parse_tnet(cls, fn, sep=' '):
    """ Grammar retro-ingennired from fb/emaileu.txt. tnet format is official ? """
    cls.log.debug('opening file: %s' % fn)
    for line in open(fn):
        line = line.strip()
        if not line:
            continue
        line1_length = line.split(sep)
        if len(line1_length) == 2:
            data_file_format = 'txt'
            v1, v2 = line.strip().split(sep)
            w = 1
            yield int(v1), int(v2), w, None
        elif len(line1_length) == 5:
            data_file_format = 'tnet'
            _line = line.strip().split(sep)
            v1, v2 = _line[-3:-1]
            w = int(_line[-1])
            if w == 0:
                continue
            else:
                yield int(v1), int(v2), w, None
