'Parse the TZ offset.
@param s: A string representation of the TZ offset.
@type s: str
@return: The signed offset in hours.
@rtype: str'

def __offset(self, s):

    if (len(s) == len('-00:00')):
        return int(s[:3])
    if (len(s) == 0):
        return self.tz.local
    if (len(s) == 1):
        return 0
    raise Exception()
