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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 append_sfixed64(self, value):
 """Appends a signed 64-bit integer to our buffer, in little-endian byte-order. """

        sign = (value & 0x8000000000000000) and -1 or 0
        if value >> 64 != sign:
            raise errors.EncodeError('SFixed64 out of range: %d' % value)
        self._stream.append_little_endian64(value & 0xffffffffffffffff)