def get_instruction(self, idx, off=None):
        """
            Get a particular instruction by using (default) the index of the address if specified

            :param idx: index of the instruction (the position in the list of the instruction)
            :type idx: int
            :param off: address of the instruction
            :type off: int

            :rtype: an :class:`Instruction` object
        """
        if off != None:
            idx = self.off_to_pos(off)
        return [i for i in self.get_instructions()][idx]