Global variable x is not defined

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Hi I don't know whether this solves your problem. But please try first to solve you spacing:

def where1(msg):
    global x1
    x1 = msg.data
def where2(msg):
    global y1
    y1 = msg.data

def ground():
    global cmd
    cmd = rospy.Publisher("/atrv/motion", Twist)
    rospy.init_node("ground")   
    rospy.Subscriber("/box_positiona", Float64, where1)
    rospy.Subscriber("/box_positionb", Float64, where2)
    print x1 # <-- *here* !!!!
    print y1 # <-- *here* !!!!
    rospy.spin() # this will block untill you hit Ctrl+C
if __name__ == '__main__':
    ground() # <-- *and here* !!!!