<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def mnemonic(self, value):
 """Set instruction mnemonic. """

        if value not in REIL_MNEMONICS:
            raise Exception("Invalid instruction mnemonic : %s" % str(value))

        self._mnemonic = value