How to get all topics ready for publishing before anything else!

Knowledgebase
1

Here is an example of how to get all your topics ready so that whenever you publish into them they will work once.

class RobotControl(object):

    def __init__(self):

        # create publishers
        # Use a queue size that works. See Reference 2 below.
        self.pub_cmd_vel = rospy.Publisher("/cmd_vel", Twist, queue_size=10)
        self.pub_take_off = rospy.Publisher("/drone/takeoff", Empty, queue_size=10)
        self.pub_land = rospy.Publisher("/drone/land", Empty, queue_size=10)

        # These are the topic you intend to get ready before anything else!
        self.pub_list = [self.pub_cmd_vel, self.pub_take_off, self.pub_land]

        # create messages to publish
        self.move = Twist()
        self.takeoff = Empty()
        self.land = Empty()

        # only if you need it. See Reference 3 below.
        self.rate = rospy.Rate(10)  

        # now get all the topics ready
        self.connect_to_all_topics()

    def connect_to_all_topics(self):
        # Wait for all topics to be ready. See Referece 1.
        for i in self.pub_list:
            while i.get_num_connections() < 1:
                rospy.loginfo("Connecting to all topics...")

        rospy.loginfo("Connected to all topics!")

References:

  1. How to publish once (only one message) into a topic and get it to work - #5
  2. ROS Publishers - what is queue_size and why is it important?
  3. Proper use of rospy.Rate or ros::Rate
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2

Iā€™m not able edit the original post.
I later realised the proper use of rospy.Rate(), and found it not needed for this purpose. I would recommend the following changes to the post:

import time

class RobotControl(object):

    def __init__(self):

        # create publishers
        # Use a queue size that works. See Reference 2 below.
        self.pub_cmd_vel = rospy.Publisher("/cmd_vel", Twist, queue_size=1)
        self.pub_take_off = rospy.Publisher("/drone/takeoff", Empty, queue_size=1)
        self.pub_land = rospy.Publisher("/drone/land", Empty, queue_size=1)

        # These are the topic you intend to get ready before anything else!
        self.pub_list = [self.pub_cmd_vel, self.pub_take_off, self.pub_land]

        # create messages to publish
        self.move = Twist()
        self.takeoff = Empty()
        self.land = Empty()

        # now get all the topics ready
        self.connect_to_all_topics()

    def connect_to_all_topics(self):
        # give ROS a second to establish the publishers
        time.sleep(1)
        # Wait for all topics to be ready. See Referece 1.
        for topic in self.pub_list:
            while topic.get_num_connections() < 1:
                rospy.loginfo("Connecting to all topics...")

        rospy.loginfo("Connected to all topics!")
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