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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def tz(self):
 """Time zone information."""


        if self.timezone is None:
            return None

        try:
            tz = pytz.timezone(self.timezone)
            return tz
        except pytz.UnknownTimeZoneError:
            raise AstralError("Unknown timezone '%s'" % self.timezone)