Passing arguments to callback in Python

asked 2016-04-09 06:29:08 -0500

steinaak
151 ●3 ●4 ●4

updated 2016-04-09 07:42:45 -0500

gvdhoorn
86574 ●283 ●1432 ●1054 http://cor.tudelft.nl/

Hi!

I have a problem passing arguments to a callback function when Subscribing a ROStopic. The code below is what I do have now. But I only received error messages when I tried to pass arguments to the callback function. I want to send two dictionaries to the callback function together with the text received on the topic called "text" in the subscriber function below. How to pass these arguments? So far I have only been receiving thousands of error messages.

def callback(data):
    rospy.loginfo(data)

def subscriber():
    rospy.init_node("listen_for_conversation",anonymous=True)
    dict_1 = {.....}
    dict_2={......}
    content = rospy.Subscriber("text",String,callback)
    rospy.spin()

Hoping for good answers!

Thanks

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36

answered 2016-04-09 08:06:14 -0500

lucasw

8729 ●137 ●239 ●256 https://github.com/lucasw

updated 2016-04-09 08:12:00 -0500

You want to use the optional callback_args parameter to Subscriber:

def callback(data, args): 
  dict_1 = args[0]
  dict_2 = args[1]
... 
sub = rospy.Subscriber("text", String, callback, (dict_1, dict_2))

Or you could put these into a class, and have the dictionaries be class member variables.

The C++ equivalent uses boost::bind http://answers.ros.org/question/12045...

Cut and paste a reasonable amount of your error messages into the question body if you need help with errors.

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THANK YOU SO MUCH!!!!! exactly what I wanted!

steinaak ( 2016-04-09 08:42:46 -0500 )edit

4

@steinaak: why did you delete the question? If @lucasw has answered your question, please just accept the answer by ticking the checkmark to the left of the answer.

gvdhoorn ( 2016-04-09 08:53:21 -0500 )edit

This is exactly what I was looking for, thanks a ton!!

Rodrigo ( 2016-07-29 11:24:16 -0500 )edit

Would have been nice if @steinaak could've done it himself, but I've accepted the answer by @lucasw, as @steinaak (and @Rodrigo) has reported that it worked for him.

gvdhoorn ( 2016-08-13 11:48:25 -0500 )edit

1

Could you please point to an example with class and members?

yossi_ov ( 2017-11-09 07:57:06 -0500 )edit

If I want to use this with message_filters.Subscriber() then how should I do it?

TrinhNC ( 2017-11-30 09:31:08 -0500 )edit

how to read 'args' parameters?

Rahul S ( 2021-03-05 11:21:38 -0500 )edit

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7

answered 2019-03-11 09:53:36 -0500

fbelmonteklein

flag of United Kingdom of Great Britain and Northern Ireland

140 ●5 ●12 ●12

updated 2019-03-11 09:54:49 -0500

Additionally to the answer presented you can use a lambda like:

def callback(data, dict_1, dict_2):
    ...
callback_lambda = lambda x: callback(x,dict_1,dict_2)
sub = rospy.Subscriber("text", String, callback_lambda)

This was useful to me since the version of ROS I was using (hydro) did not seem to have callback_args (see http://docs.ros.org/melodic/api/rospy... ) implemented yet.

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1

This a very elegant solution and also thanks for pointing out it solves the issue on hydro.

bruno.rosa ( 2019-06-17 04:10:36 -0500 )edit

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