rosparam: Different output format on vectors

edit

When running the same ros package on different machines, I'm facing an issue with the rosparam get output syntax.

In most cases, I get the vector syntax, but on one machine I get the list syntax as described here.

Machine 1 (List)

user@machine1:~/foo$ rosparam get /my_grp/my_var
- 1.5
- 2.5
- 2.8
- 2.5

Machine 2 (Vector)

user@machine2:~/foo$ rosparam get /my_grp/my_var
[1.5, 2.5, 2.8, 2.5]

Since I'm parsing the output in a bash script, this difference raises further issues.

I'm running the same version of python-yaml on both machines

python-yaml/xenial,now 3.11-3build1 amd64 [installed,automatic]

ROS-kinetic-rosparam is the same:

ros-kinetic-rosparam/xenial,now 1.12.17-1xenial-20201103-022214+0000 amd64 [installed,automatic]

Furthermore, when setting a parameter on machine 1, I get a yaml warning:

user@machine1:~/foo$ rosparam set /my_grp/my_var_scalar 2
/opt/ros/kinetic/lib/python2.7/dist-packages/rosparam/__init__.py:375: YAMLLoadWarning: calling yaml.load() without Loader=... is deprecated, as the default Loader is unsafe. Please read https://msg.pyyaml.org/load for full details.
  set_param_raw(param, yaml.load(value), verbose=verbose)

What's the reason for different outputs of rosparam? Thanks in advance

Update 2020-12-08

I've further checked the yaml by running following piece of python code on both machines

import yaml as y
print(y.__version__)

Which returns 3.11 on machine 2 and 5.1.1 on machine 2. As mentioned above the apt package is 3.1.1 on both machines. Furthermore, on machine 2, there is PyYAML installed within pip.

So, i would like to rephrase the question: Whats the correct way to define the version of python-yaml (resp. PyYAML) to be used within ROS kinetic?