accessing a variable from outside the function in python

Question

#!/usr/bin/env python
import roslib
import rospy
import time
from nav_msgs.msg import Odometry 

def position_callback(data):
    global q2
    q2=data.pose.pose.position.x
    q1=data.pose.pose.position.y
    q3=data.pose.pose.position.z


def position():      
    rospy.init_node('position', anonymous=True)  #initialize the node"
    rospy.Subscriber("odom", Odometry, position_callback)

if __name__ == '__main__':

    try:
        position()
        print q2
        rospy.spin()
    except rospy.ROSInterruptException: pass

the error i get is like this:

print q2
NameError: global name 'q2' is not defined

I defined q2 as global variable already.

falsetru · Accepted Answer · 2014-11-03 14:36:04Z

2

Declaring q2 as a global variable does make the global variable exist.

Actually calling the function and execution of the assignment statement q2 = ... cause the creation of the variable. Until then, the code cannot access the variable.

position function does not call the position_callback, but pass it to rospy.Subscriber (which probably register the callback function, and not call it directly).

Initialize q2 if you want to access the variable before it is set.

q2 = None

def position_callback(data):
    global q2
    q2 = data.pose.pose.position.x
    q1 = data.pose.pose.position.y
    q3 = data.pose.pose.position.z

edited Nov 3, 2014 at 14:36

answered Nov 3, 2014 at 14:30

falsetru

371k69 gold badges769 silver badges659 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Ruthvik Vaila Over a year ago

no.i want to actually access the value..its not for printing..i want to use this value in some other function.

falsetru Over a year ago

@RuthvikVaila, Initialize the variable q2 to some value that represent null value if you want to access the variable before the callback is called. I updated the answer accordingly.

Yair Daon · Accepted Answer · 2014-11-03 14:34:01Z

0

You never initialize q2. It cannot have a value. Try to define it in global scope - after the imports. Then call it iniside the functionposition().

answered Nov 3, 2014 at 14:34

Yair Daon

1,1632 gold badges15 silver badges28 bronze badges

Collectives™ on Stack Overflow

accessing a variable from outside the function in python

2 Answers 2

2 Comments

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related