pass python objects in ROS messages and services

Question

Is there a way to define a ROS message or service with arbitrary python objects? Is the only option to use a string and use json.dumps / json.loads?

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Originally posted by waspinator on ROS Answers with karma: 122 on 2018-01-19

Post score: 0

Answer 1

Is there a way to define a ROS message or service with arbitrary python objects?

Assuming you mean: can I have fields with types of 'arbitrary Python types', then: no.

Is the only option to use a string and use json.dumps / json.loads?

Don't know whether it's the only way, but it is a way.

Can you clarify why you'd want to do this?

It's a really heavy and invasive form of coupling, which limits reusability of your components.

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Originally posted by gvdhoorn with karma: 86574 on 2018-01-19

This answer was ACCEPTED on the original site

Post score: 1

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Original comments

Comment by waspinator on 2018-01-20:
I use a python ORM to read/write to a database, and I was considering having a ROS node with services for each database operation. I could a) send the python object to the service to save, b) send just the properties and have the service create a new object, or c) use the ORM directly. not sure.

Comment by gvdhoorn on 2018-01-21:
In any case: ROS 1 msg IDL only supports primitive types or composites of those types. See wiki/msg.