'Difference to Greenwich time in hours; e.g. \'+0200\', \'-0430\'.
If timezone information is not available, return an empty string.'

def O(self):

    if (not self.timezone):
        return ''
    seconds = self.Z()
    if (seconds == ''):
        return ''
    sign = ('-' if (seconds < 0) else '+')
    seconds = abs(seconds)
    return ('%s%02d%02d' % (sign, (seconds // 3600), ((seconds // 60) % 60)))
