How to recieve information from a subscriber withouth executing a callback

edit

I have the following code:

#!/usr/bin/env python
import rospy
from std_msgs.msg import  Float64
from random import randint
from time import sleep
from std_msgs.msg import Int64

def counter(msg):

        print msg.data

rospy.init_node('Arduino_hear_my_whispers')
pub = rospy.Publisher('your_topic', Float64, queue_size=10)
while not rospy.is_shutdown():
        rnd = 1.0
        print "the number is " + str(rnd)
        message=Float64(rnd)
        pub.publish(message)
        sleep(0.01)
        rnd = 2.0
        print "the number is " + str(rnd)
        message=Float64(rnd)
        pub.publish(message)
        sleep(0.01)
        sub = rospy.Subscriber('I_know', Int64, counter, queue_size=100)

rospy.spin()

I am using this code to receive some signals from Arduino. The signals are sended to the topic "I_know". Although the code is running properly, I wonder if there is a way to get the signals from the topic without executing the callback? Just assigning the values from the topic to a variable from the main program.