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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 verify(self):
 """ Verifies that the request timestamp is not beyond our allowable timestamp mismatch and that the request signature matches our expectations. """

        try:
            if self.timestamp_mismatch is not None:
                m = _iso8601_timestamp_regex.match(self.request_timestamp)
                year = int(m.group("year"))
                month = int(m.group("month"))
                day = int(m.group("day"))
                hour = int(m.group("hour"))
                minute = int(m.group("minute"))
                second = int(m.group("second"))

                req_ts = datetime(year, month, day, hour, minute, second)
                now = datetime.utcnow()

                if abs(req_ts - now) > timedelta(0, self.timestamp_mismatch):
                    raise InvalidSignatureError("Timestamp mismatch")

            if self.expected_signature != self.request_signature:
                raise InvalidSignatureError(
                    "Signature mismatch: expected %r, got %r" % (
                        self.expected_signature, self.request_signature))
        except (AttributeError, KeyError, ValueError) as e:
            raise InvalidSignatureError(str(e))

        return True