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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 read_var_uint64(self):
 """Reads a varint from the stream, interprets this varint as an unsigned, 64-bit integer, and returns the integer. """

        i = self._read_varint_helper()
        if not 0 <= i <= wire_format.UINT64_MAX:
            raise errors.DecodeError('Value out of range for uint64: %d' % i)
        return i