Python3 supported?

[fnoop]

Issue details

Traceback (most recent call last):
  File "./test-rosparams", line 13, in <module>
    param_received, param_list = param_get_all(False)
  File "/opt/ros/kinetic/lib/python2.7/dist-packages/mavros/param.py", line 167, in param_get_all
    sorted((Parameter(k, v) for k, v in params.iteritems()),
AttributeError: 'dict' object has no attribute 'iteritems'

param_get_all() function fails as python3 doesn't have iteritems. Possible solutions are to change to items() or import iteritems from future:
from future.utils import iteritems

MAVROS version and platform

Mavros: 0.22
ROS: Kinetic
Ubuntu: 16.04

Autopilot type and version

[ x ] ArduPilot
[ ] PX4

Version: 3.5

[vooon]

Not officially supported, ROS still uses 2.7.
2to3 may help.

[fnoop]

This is still a problem. From:
http://www.ros.org/reps/rep-0003.html#python

Melodic
Ubuntu will most likely stop supporting Python 2 in release 20.04. To make sure ROS will be able to support that version of Ubuntu, ROS Python packages starting with Melodic Morenia are highly encouraged to support both Python 2.7 and Python 3.5 or later. During the development of Melodic there will be work undertaken to support both Python 2 and Python 3 (including rosdep keys) so ROS package developers can more easily test with either version of Python.

Python 2 EOL is fast approaching, and there are quite a few python modules/frameworks that really depend on Python 3 or at least significantly encourage them (through nice features only available in Python 3). We are currently writing a full web GCS which significantly leverages MAVROS, however we are having to move to Python 3 to follow support of other libraries/frameworks and the lack of Python 3 support in MAVROS is a dealbreaker. ROS 2 would be an option as it only supports Python 3, but MAVROS does not support ROS 2 either.
Is there any plan or timeline for MAVROS to support Python 3 and/or ROS 2?

[khancyr]

Hello,

Using futur, the support for python3 shouldn't be long as MAVROS don't have much pure python code. I will see to do it this weekend!

[fnoop]

@khancyr How do you deal with something like the error in this issue? Because in this case 'params' is from:
params = rospy.get_param(mavros.get_topic('param'))
So the params object doesn't have iteritems - it doesn't do any good importing iteritems in mavros/param.py from future.utils or six.

[fnoop]

Useful cheat sheet: http://python-future.org/compatible_idioms.html

Option 2 for items() seems most suitable for this situation:

# Python 2 and 3: option 2
from future.utils import viewitems
for (key, value) in viewitems(heights):   # also behaves like a set

Option 1 is inefficient, Option 2 doesn't work because of the above

[fnoop]

Now getting:

[dev] [mav@goodrobots ~/code/ros]$ ./test-py3.py
Traceback (most recent call last):
  File "./test-py3.py", line 21, in <module>
    param_received, param_list = param_get_all(False)
  File "/opt/ros/melodic/lib/python2.7/dist-packages/mavros/param.py", line 170, in param_get_all
    cmp=lambda x, y: cmp(x.param_id, y.param_id))
TypeError: 'cmp' is an invalid keyword argument for this function

Need to convert old cmp param to key: https://docs.python.org/3/library/functools.html#functools.cmp_to_key

Importing these in mavros/param.py:

from past.builtins import cmp
import functools

And then changing the sorted param in param_get_all() return to:

            sorted((Parameter(k, v) for k, v in viewitems(params)),
                   key=functools.cmp_to_key(lambda x, y: cmp(x.param_id, y.param_id)))
            )

Fixes and works in both python2 and python3 - a little messy, maybe there's a cleaner method.

[fnoop]

Raised PR here with fix:
#1127

[vooon]

Unfortunately i do not have any plans. In my current project i just use 3.6+...
I think that usage of .items() is good enough.

[amilcarlucas]

The PR is now merged, can this be closed?

[fnoop]

Yes, working great in python3 now. Thanks :)