ImportError: No module named robot_messages.msg

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When I run this code I get :

ImportError: No module named robot_messages.msg

This is the code that is written on this tutorial: https://www.youtube.com/watch?v=DLVyc... and the person is able to run it at 27:50 min mark, but I am not.

I have no idea what could be the problem. I made two packages. One by the name location_monitor and other by the name robot_messages. In the robot_messages I made file LandmarkDistance.msg which looks like this:

string name # Name of the landmark
float64 location # distance from landmark in meters

I tried searching for the forum and making a seperate package just for the messages, but I just don't know what the problem could be.

#!/usr/bin/env python

import math
import rospy
from nav_msgs.msg import Odometry
from robot_messages.msg import LandmarkDistance


    def distance(x1,y1,x2,y2):

        xd=x1-x2
        yd=y1-y2
    return math.sqrt(xd*xd+yd*yd)   

class LandmarkMonitor(object):
    def __init__(self, pub, landmarks):
        self._pub=pub
        self._landmarks= landmarks

    def callback(self,msg):
        x=msg.pose.pose.position.x
        y=msg.pose.pose.position.y
        z=msg.pose.pose.position.z

        closest_name= None
        closest_distance= None

        for l_name, l_x, l_y in self._landmarks:
            dist=distance(x,y,l_x,l_y)
            if closest_distance is None or dist < closest_distance:
                closest_name = l_name
                closest_distance = dist

        ld= LandmarkDistance()
        ld.name= closest_name
        ld.distance= closest_distance
        self._pub.publish(ld)
        rospy.loginfo('closest: {} and the distance is {}' .format(closest_name,closest_distance))


def main():
    rospy.init_node('location_monitor')
    landmarks= []
    landmarks.append(("Cube", 0.31,-0.99))
    landmarks.append(("Dumpster", 0.11,-2.42))
    landmarks.append(("Cylinder", -1.14,-2.88))
    landmarks.append(("Barrier", -2.59,-0.83))
    landmarks.append(("Bookshelf", -0.09,0.53))

    pub= rospy.Publisher('closest_landmark', LandmarkDistance)
    monitor= LandmarkMonitor(pub, landmarks)


    rospy.Subscriber("/odom", Odometry, monitor.callback)
    # spin() simply keeps python from exiting until this node is stopped
    rospy.spin()

if __name__ == '__main__':
    main()