i want my robot to do simple calculation like addition or subtraction on my voice command how to proceed ? :( the code that i am trying is as follow

!/usr/bin/env python

import roslib; roslib.load_manifest('pi_speech_tutorial') import rospy

from time import gmtime, strftime from geometry_msgs.msg import Twist from std_msgs.msg import String from math import copysign import re

Small = { 'zero': 0, 'one': 1, 'two': 2, 'three': 3, 'four': 4, 'five': 5, 'six': 6, 'seven': 7, 'eight': 8, 'nine': 9, 'ten': 10, 'eleven': 11, 'twelve': 12, 'thirteen': 13, 'fourteen': 14, 'fifteen': 15, 'sixteen': 16, 'seventeen': 17, 'eighteen': 18, 'nineteen': 19, 'twenty': 20, 'thirty': 30, 'forty': 40, 'fifty': 50, 'sixty': 60, 'seventy': 70, 'eighty': 80, 'ninety': 90 }

Magnitude = { 'thousand': 1000, 'million': 1000000, 'billion': 1000000000, 'trillion': 1000000000000, 'quadrillion': 1000000000000000, 'quintillion': 1000000000000000000, 'sextillion': 1000000000000000000000, 'septillion': 1000000000000000000000000, 'octillion': 1000000000000000000000000000, 'nonillion': 1000000000000000000000000000000, 'decillion': 1000000000000000000000000000000000, }

class TalkBack:

def __init__(self):

# def __init__(self, msg): # Exception.__init__(self, msg) rospy.on_shutdown(self.cleanup)

    self.voice = rospy.get_param("~voice", "voice_don_diphone")
    self.wavepath = rospy.get_param("~wavepath", "")

    # Create the sound client object
    self.soundhandle = SoundClient()

    rospy.sleep(1)
    self.soundhandle.stopAll()

    # Announce that we are ready for input
    self.soundhandle.playWave(self.wavepath + "/R2D2a.wav")
    rospy.sleep(1)
    self.soundhandle.say("Ready", self.voice)

    rospy.loginfo("Say commands...")

    # Subscribe to the recognizer output
    rospy.Subscriber('/recognizer/output', String, self.talkback)


    # A mapping from keywords to commands.
    self.keywords_to_command = {'plus': ['addition', 'add'],
                                'minus': ['subtraction', 'subtract'],
                                'devide': ['devision', 'by'],
                                'multiply': ['multiplication', 'into'],
                                }

   # rospy.loginfo("Ready to receive voice commands")



def get_command(self, data):
for (command, keywords) in self.keywords_to_command.iteritems():
        for word in keywords:
            if data.find(word) > -1:
                return command


def text2num(self, s):
a = re.split(r"[\s-]+", s)
    n = 0
    g = 0
    for w in a:
        x = Small.get(w, None)
        if x is not None:
            g += x
        elif w == "hundred":
            g *= 100
        else:
            x = Magnitude.get(w, None)
            if x is not None:
                n += g * x
                g = 0
            else:
                raise NumberException("Unknown number: "+w)
return n + g

def talkback(self, msg):        
    command = msg.data
    rospy.loginfo("Command: " + msg.data)

    if 'plus' in command.split():
    var1,var2= command.split("plus")
        var1 = self.text2num(var1)
    var2 = self.text2num(var2)
    var3=sum(var1,var2)
    self.soundhandle.say(var3, self.voice)


    else:
        return

 def cleanup(self):
    # When shutting down be sure to stop the robot!  Publish a Twist message consisting of all zeros.
rospy.loginfo("Shutting down talkback node...")

if __name__=="__main__": rospy.init_node('talkback')

try:
    TalkBack()
rospy.spin()

except:
    pass