'Try to send an SNMP GET operation using SNMPv3 for the specified OID.
Parameters
oid : str
The SNMP OID that you want to get.
Returns
string : str
The string as part of the value from the OID you are trying to retrieve.'

def _get_snmpv3(self, oid):

    snmp_target = (self.hostname, self.snmp_port)
    cmd_gen = cmdgen.CommandGenerator()
    (error_detected, error_status, error_index, snmp_data) = cmd_gen.getCmd(cmdgen.UsmUserData(self.user, self.auth_key, self.encrypt_key, authProtocol=self.auth_proto, privProtocol=self.encryp_proto), cmdgen.UdpTransportTarget(snmp_target, timeout=1.5, retries=2), oid, lookupNames=True, lookupValues=True)
    if ((not error_detected) and snmp_data[0][1]):
        return str(snmp_data[0][1])
    return u''
