Module 2: Python3 for Robotics

A note on this document

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Computer Player

We will now implement a computer player node that will send a random choice to the player node.

First import your required modules:

import rospy, random
from std_msgs.msg import String

Here, we are importing two modules: rospy, which allows us to run ROS code in Python, and the String message from the std_msgs ROS package.

class Computer:
    # class constant to store computer choices
    CHOICES = ['Rock', 'Paper', 'Scissors']
    
    # initialize class
    def __init__(self,):
        # instance variables
        self.computers_choice = String()
        
        # subscriber to receive the computer's choice over the computer topic
        rospy.Subscriber('user_choice', String, self.callback_computers_choice)
        
        # publisher to send player's choice over the player topic
        self.pub = rospy.Publisher('computer_choice', String, queue_size=1)
    
    def callback_computers_choice(self, data):
        # use random module imported earlier to select a random index from the list
        rand_index = random.randint(0,len(self.CHOICES)-1)
        # use the index to select an item from the list
        self.computers_choice = self.CHOICES[rand_index]
        self.pub.publish(self.computers_choice)

rospy.init_node('computer')
Computer()
rospy.spin()

Now return to the Module3_Python3 User Notebook and fill in the requested inputs.