I'm getting the rosgraph not found error

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Hello, I'm trying to control a robot that has ROS controllers with a Python program, but everytime I run the program, I get an error regarding the rosgraph library not being found. I've tried everything other people have said in other threads, but nothing has worked so far. This is the program I'm using to try and control the robot:

#! /usr/bin/env python
import rospy, math
import numpy as np
import sys, termios, tty, select, os
from geometry_msgs.msg import Twist


class KeyTeleop(object):
    cmd_bindings = {'q': np.array([1, 1]),
                    'w': np.array([1, 0]),
                    'e': np.array([1, -1]),
                    'a': np.array([0, 1]),
                    'd': np.array([0, -1]),
                    'z': np.array([-1, -1]),
                    'x': np.array([-1, 0]),
                    'c': np.array([-1, 1])
                    }
    set_bindings = {'t': np.array([1, 1]),
                    'b': np.array([-1, -1]),
                    'y': np.array([1, 0]),
                    'n': np.array([-1, 0]),
                    'u': np.array([0, 1]),
                    'm': np.array([0, -1])
                    }

    def init(self):
        # Save terminal settings
        self.settings = termios.tcgetattr(sys.stdin)
        # Initial values
        self.inc_ratio = 0.1
        self.speed = np.array([0.5, 1.0])
        self.command = np.array([0, 0])
        self.update_rate = 10  # Hz
        self.alive = True
        # Setup publisher
        self.pub_twist = rospy.Publisher('/cmd_vel', Twist)

    def fini(self):
        # Restore terminal settings
        termios.tcsetattr(sys.stdin, termios.TCSADRAIN, self.settings)

    def run(self):
        try:
            self.init()
            self.print_usage()
            r = rospy.Rate(self.update_rate)  # Hz
            while not rospy.is_shutdown():
                ch = self.get_key()
                self.process_key(ch)
                self.update()
                r.sleep()
        except rospy.exceptions.ROSInterruptException:
            pass
        finally:
            self.fini()

    def print_usage(self):
        msg = """
    Keyboard Teleop that Publish to /cmd_vel (geometry_msgs/Twist)
    Copyright (C) 2013
    Released under BSD License
    --------------------------------------------------
    H:       Print this menu
    Moving around:
      Q   W   E
      A   S   D
      Z   X   Z
    T/B :   increase/decrease max speeds 10%
    Y/N :   increase/decrease only linear speed 10%
    U/M :   increase/decrease only angular speed 10%
    anything else : stop

    G :   Quit
    --------------------------------------------------
    """
        self.loginfo(msg)
        self.show_status()

    # Used to print items to screen, while terminal is in funky mode
    def loginfo(self, str):
        termios.tcsetattr(sys.stdin, termios.TCSADRAIN, self.settings)
        print(str)
        tty.setraw(sys.stdin.fileno())

    # Used to print teleop status
    def show_status(self):
        msg = 'Status:\tlinear %.2f\tangular %.2f' % (self.speed[0], self.speed[1])
        self.loginfo(msg)

    # For everything that can't be a binding, use if/elif instead
    def process_key(self, ch):
        if ch == 'h':
            self.print_usage()
        elif ch in self.cmd_bindings.keys():
            self.command = self.cmd_bindings[ch]
        elif ch in self.set_bindings.keys():
            self.speed = self.speed * (1 + self.set_bindings[ch] * self.inc_ratio)
            self.show_status()
        elif ch == 'g':
            self.loginfo('Quitting')
            # Stop the robot
            twist = Twist()
            self.pub_twist.publish(twist)
            rospy.signal_shutdown('Shutdown')
        else:
            self.command = np.array([0, 0])

    def update(self):
        if rospy.is_shutdown():
            return
        twist = Twist()
        cmd = self.speed * self.command
        twist.linear.x = cmd[0]
        twist.angular.z = cmd[1]
        self.pub_twist.publish(twist)

    # Get input from the terminal
    def get_key(self):
        tty.setraw(sys.stdin.fileno())
        select.select([sys.stdin], [], [], 0)
        key ...