Use rospy with virtualenv in Python3

Introduction

ROS Advent Calendar 2019 This is the article on the 23rd day. There are only 8 days left until the EOL of Python2, but are you all done with Python3? This time, I tried to make it possible to execute rospy of ROS1 with virtualenv of Python3, so I would like to introduce it.

In order to use the official ROS1 rospy, there are the following environmental restrictions.

1. Use Ubuntu
2. Install ROS
3. Use the Python2 / library installed on your system

this is I want to make ROS1 coexist with an existing Python project (Python3) using pip. b. I want to try rospy on MacOS for a moment

It is inconvenient in such cases.

There is also roslibpy as a solution, but since rosbridge bridges the communication once with websocket, It takes a lot of communication overhead. Therefore, the ROS code related to rospy is written only in Python, and by preparing PyPI (Python Package Index) that can install rospy as a pure Python package, even in Python3 I tried to use rospy.

How to use

We have confirmed in the following environment.

• OS: Ubuntu 18.04
• Python: Python3.6.7

Here is a sample of how to use virtualenv. No ROS installation required. (Basically the same for pipenv etc.)

virtualenv -p python3 venv
. ./venv/bin/activate
pip install --extra-index-url https://rospypi.github.io/simple rospy-all

If you want to use TF2 or cv_bridge, add more

pip install --extra-index-url https://rospypi.github.io/simple cv_bridge tf2_ros

You can do it.

Prepare the following sample

talker.py

import rospy
import std_msgs.msg

rospy.init_node("talker")
pub = rospy.Publisher("chat", std_msgs.msg.String, queue_size=1)
rate = rospy.Rate(2)
while not rospy.is_shutdown():
    pub.publish("hello")
    rate.sleep()

listner.py

import rospy
import std_msgs.msg

def callback(msg):
    print(msg.data)

rospy.init_node("listener")
rospy.Subscriber("chat", std_msgs.msg.String, callback)
rospy.spin()

Install additional rosmaster

pip install --extra-index-url https://rospypi.github.io/simple rosmaster defusedxml

From each of the three terminals

1. First, start rosmaster.

   . ./venv/bin/activate
   rosmaster --rcore
   

2. Next, start the talker node.

   . ./venv/bin/activate
   export ROS_MASTER_URI=http://localhost:11311
   python talker.py
   

3. Finally, start the listener node.

   . ./venv/bin/activate
   export ROS_MASTER_URI=http://localhost:11311
   python listener.py
   

4. If you can see the Subscirbe topic in the last listener node for the following, it is successful.

   $ python listener.py
   WARNING: cannot load logging configuration file, logging is disabled
   hello
   hello
   hello
   hello
   hello
   

Now you can write ROS nodes only in Python 3 without installing ROS. We have confirmed that the same thing can be done on MacOS.

About the contents

• PyPI can be created as long as it can host static files (PEP53)
• Packages such as tf2_py, PyKDL, cv_bridge are Python packages that require a c ++ build, but a little do your best ROS Can be executed independently of runtime

I'm doing something like that.

in conclusion

The PyPI I prepared this time was made as a hobby by myself, and I don't know how much it can support, but I think it's convenient to use for a while, so please give it a try. https://github.com/rospypi/simple

I want to be able to release it officially ...

Let's enjoy robot programming!