Hello. I use python. I want to use the loop based on data of Publisher. For example, If I get the data == 1, I need to print "Hello" every 3 seconds, until when I will receive the new message with another data. Please help me.
Originally posted by Tvlad on ROS Answers with karma: 35 on 2016-09-01
Post score: 0
Subscriber callbacks run on their own thread, so I usually update a variable in the subscriber callback and then use that data in a main loop running in the startup thread. Something like this:
import rospy
class MyNode:
def main(self):
rospy.subscriber('sometopic', SomeMsgType, self.msgCallback)
self.value = None
self.rate = rospy.getParam('~rate', 10.0)
while not rospy.is_shutdown():
... do something with self.value ...
rate.sleep()
def msgCallback(self, newValue):
self.value = newValue
if name == 'main':
try:
MyNode().main()
except rospy.ROSInterruptException:
pass
Originally posted by Mark Rose with karma: 1563 on 2016-09-01
This answer was ACCEPTED on the original site
Post score: 4
Comment by Tvlad on 2016-09-05:
Thank you, but I have a question. For what we use the line:
self.value = None
And, Can I use the loop like this:
while self.value == "data":
Sorry If it's the stupid questions.
Comment by Mark Rose on 2016-09-06:
You have to set a value for self.value before the while loop runs. Python will throw an exception if you try to access an attribute that doesn't exist. I just chose None so you can determine that no value has been received yet. I'm not sure if I understand your loop question.
Comment by Mark Rose on 2016-09-06:
The main loop must be while not rospy.is_shutdown() so that you will exit if the ROS core shuts down. You'll probably want to check for None within the loop:
if self.value is not None:
... do something ...
Comment by Mark Rose on 2016-09-06:
You should read the rospy tutorials. Start with the first one.