Problem with yaml

edit

Hi, I use ROS Indigo on Raspbian. When I try turn on a program, I have got error:

    Traceback (most recent call last):
  File "/home/pi/ros_catkin_ws/src/hil/scripts/hil.py", line 2, in <module>
    import rospy
  File "/home/pi/ros_catkin_ws/devel/lib/python2.7/dist-packages/rospy/__init__.py", line 35, in <module>
    exec(__fh.read())
  File "<string>", line 49, in <module>
  File "/home/pi/ros_catkin_ws/src/ros_comm/rospy/src/rospy/client.py", line 47, in <module>
    import yaml
ImportError: No module named 'yaml'

My program code is:

    #!/usr/bin/python3
import rospy
from std_msgs.msg import String
#added
from geometry_msgs.msg import Twist 


def callback(data):
    global msg
    if data.data=="Unknown":
        pub = rospy.Publisher('cmd_vel', Twist) 
        rospy.loginfo("Classifiers output: %s in unknown" % data.data)
        msg.linear.x = 2
        msg.linear.y = 2
        msg.angular.z = 0
        speed = 0.4 
        rospy.loginfo("checking for cmd" + str(msg.linear))
        pub.publish(msg)
    elif data.data=="Check":
        rospy.loginfo("Classifiers output: %s in check" % data.data)
    else:      
        rospy.loginfo("Classifiers output: %s and not unknown or check" % data.data)



def listener():

     global msg
     rospy.init_node('listener', anonymous=True)
     msg = Twist()
     rospy.Subscriber("ccc", String, callback)
     rospy.spin()


if __name__ == '__main__':



    listener()

I tried

sudo apt-get install python-yaml

yaml is installed, but error still appears

Thanks