error_callback when using apply_async in python 2.7

[Elizabeth Clark]

When I call rvic.parameters.parameters with multiple cores in Python 2.7.11, I get the following error:

INFO:parameters>> On Outlet 1 of 1
ERROR:write>> Traceback (most recent call last):
ERROR:write>> File "run_rvic.py", line 62, in
ERROR:write>> main()
ERROR:write>> File "run_rvic.py", line 56, in main
ERROR:write>> rvic.parameters.parameters(param_cfg_name, numofproc=cores)
ERROR:write>> File "/d6/eclark/miniconda2/envs/otl_env/lib/python2.7/site-packages/rvic-1.1.0-py2.7-linux-x86_64.egg/rvic/parameters.py", line 73, in parameters
ERROR:write>> error_callback=error)
ERROR:write>> TypeError
ERROR:write>> :
ERROR:write>> apply_async() got an unexpected keyword argument 'error_callback'

Apparently error_callback is not a keyword option for apply_async in python 2 (ref). In this case, it looks like nothing happens if there is an error; the callback just isn't called. I can think of 3 options for how to handle this:

1. Put in a python version check that disables multiprocessing for python 2.
2. Make a function that only uses error_callback if user is using python 3. Set up an error check in the stat return value of apply_async to show if the job completed or not. The problem, of course, being that you don't get the error code from gen_uh_run.
3. Add something like this traceback function to gen_uh_run.

[Bart Nijssen]

My vote is for 1) since there is no good reason to keep everything compatible with python 2.

[Joe Hamman]

I think we can just leave out the error_callback argument in python 2.7.

Some psudo code:

def _make_async_kwargs():
    kwargs = dict(callback=store_result)
    if py3:
        kwargs['error_callback'] = error
    return kwargs

        kwargs = _make_async_kwargs()
        for i, (key, outlet) in enumerate(iteritems(outlets)):
            log.info('On Outlet #%s of %s', i + 1, len(outlets))
            stat = pool.apply_async(gen_uh_run,
                                    (uh_box, fdr_data, fdr_vatts,
                                     dom_data, outlet, config_dict,
                                     directories),
                                    **kwargs)

@lizaclark - do you know if stat.get() will raise an error in Python 2?