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Tutlesim GO2GOAL python code error : TypeError: unsupported operand type(s) for -: 'str' and 'float' [closed]

asked 2020-11-03 12:54:11 -0500

I tried the following code from Turtlesim tutorial (GO TO GOAL):

import rospy
from geometry_msgs.msg import Twist
from turtlesim.msg import Pose
from math import pow, atan2, sqrt

class TurtleBot:

    def __init__(self):

        rospy.init_node('turtlebot_controller', anonymous=True)
        self.velocity_publisher = rospy.Publisher('/turtle1/cmd_vel',Twist, queue_size=10)
        self.pose_subscriber = rospy.Subscriber('/turtle1/pose',Pose, self.update_pose)
        self.pose = Pose()
        self.rate = rospy.Rate(10)

    def update_pose(self,data):

        self.pose = data
        self.pose.x = round(self.pose.x, 4)
        self.pose.y = round(self.pose.y, 4)

    def euclidean_distance(self, goal_pose):

            return sqrt(pow((goal_pose.x - self.pose.x), 2) + pow((goal_pose.y - self.pose.y), 2))

    def linear_vel(self, goal_pose, constant = 1.5):

        return constant * self.euclidean_distance(goal_pose)

    def steering_angle(self, goal_pose):

        return atan2(goal_pose.y - self.pose.y, goal_pose.x - self.pose.x)

    def angular_vel(self, goal_pose, constant = 6):

        return constant * (self.steering_angle(goal_pose) - self.pose.theta)

    def move2goal(self):

        goal_pose = Pose()

        goal_pose.x = input("Set your x goal: ")
        goal_pose.y = input("Set your y goal: ")

        distance_tolerance = input("Set your tolerance: ")

        vel_msg = Twist()

        while self.euclidean_distance(goal_pose) >= distance_tolerance:

            vel_msg.linear.x = self.linear_vel(goal_pose)
            vel_msg.linear.y = 0
            vel_msg.linear.z = 0

            vel_msg.angular.x = 0
            vel_msg.angular.y = 0
            vel_msg.angular.z = self.angular_vel(goal_pose)



        vel_msg.linear.x = 0
        vel_msg.linear.z = 0


if __name__ == '__main__':

        x = TurtleBot()

    except rospy.ROSInterruptException:

When i run it, it asks for value of x, value of y and then value of tolerance. But after entering tolerance it shows this error:

Traceback (most recent call last):
  File "/home/paul_pavish/draw_arm/devel/lib/turtle_control/", line 15, in <module>
    exec(compile(, python_script, 'exec'), context)
  File "/home/paul_pavish/draw_arm/src/turtle_control/", line 82, in <module>
  File "/home/paul_pavish/draw_arm/src/turtle_control/", line 57, in move2goal
    while self.euclidean_distance(goal_pose) >= distance_tolerance:
  File "/home/paul_pavish/draw_arm/src/turtle_control/", line 29, in euclidean_distance
    return sqrt(pow((goal_pose.x - self.pose.x), 2) + pow((goal_pose.y - self.pose.y), 2))
TypeError: unsupported operand type(s) for -: 'str' and 'float'

I assume that the goal_pose = Pose() didn't do it's part. If yes, then that means that import from a different module from turtlesim.msg import Pose didn't work. I tried simple Publisher & Subscriber (it worked) and Turtlesim_teleop_key(it also worked) along with some other customisations on Publisher & Subscriber (worked). Then whats happening here ???

Any suggestions on how to fix this TypeError ? I tried converting ever pose related object/variable to float , and it seems working fine then, but that's not the answer for long run, . Need Help ASAP.

Thanks in advance

Paul Pavish

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Closed for the following reason the question is answered, right answer was accepted by Paul Pavish
close date 2020-11-10 11:50:20.483687

1 Answer

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answered 2020-11-03 17:02:26 -0500


goal_pose.x = input("Set your x goal: ")
goal_pose.y = input("Set your y goal: ")


goal_pose.x = float(input("Set your x goal: "))
goal_pose.y = float(input("Set your y goal: "))

This should resolve the issue.

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Thanks @skpro19, Yes it did work . But then what happened to the goal_pose=Pose() , why it didn't work? or if this is the actual method for float input, then why is it wrong in the ROS Turtlesim Go To Goal tutorial ?

I'm just trying to understand.

Thanks & Regards Paul Pavish

Paul Pavish gravatar image Paul Pavish  ( 2020-11-04 01:35:36 -0500 )edit

I don't think there's an issue with goal_pose = Pose(). It is just that the way you were taking the input earlier was causing Python to think that x and y are Strings.

skpro19 gravatar image skpro19  ( 2020-11-04 15:19:44 -0500 )edit

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Asked: 2020-11-03 12:53:16 -0500

Seen: 95 times

Last updated: Nov 03 '20