Error when issuing ncks command, unexpected bytes object instead of string

Question

When I issue an NCO call usign pynco for ncks I am getting an error, it looks like a bytes object is being sent instead of a string, resulting in this:

pydev debugger: starting (pid: 7864)
2018-02-05  11:30:53 INFO Start time:    2018-02-05 11:30:53.365789
Error in calling operator ncks with:
>>> C:/home/miniconda/pkgs/nco-4.7.1-vc14_0/Library/bin\ncks --dmn=lon,0,20,1 --output=C:/home/data/nclimgrid/work\nclimgrid_lowres_prcp_slice00.nc C:/home/data/nclimgrid/nclimgrid_lowres_prcp.nc <<<
Inputs: C:/home/data/nclimgrid/nclimgrid_lowres_prcp.nc
b''
2018-02-05  11:36:19 ERROR Failed to complete
Traceback (most recent call last):
  File "C:\Users\DELL\git\process_grid\process_grid.py", line 949, in <module>
    options=slice_option)
  File "C:\home\miniconda\lib\site-packages\nco\nco.py", line 277, in get
    raise NCOException(**retvals)
nco.nco.NCOException: (returncode:3221225781) b''
Traceback (most recent call last):
  File "C:\home\eclipse\neon\eclipse\plugins\org.python.pydev_6.2.0.201711281614\pysrc\pydevd.py", line 1621, in <module>
    main()
  File "C:\home\eclipse\neon\eclipse\plugins\org.python.pydev_6.2.0.201711281614\pysrc\pydevd.py", line 1615, in main
    globals = debugger.run(setup['file'], None, None, is_module)
  File "C:\home\eclipse\neon\eclipse\plugins\org.python.pydev_6.2.0.201711281614\pysrc\pydevd.py", line 1022, in run
    pydev_imports.execfile(file, globals, locals)  # execute the script
  File
"C:\home\eclipse\neon\eclipse\plugins\org.python.pydev_6.2.0.201711281614\pysrc\_pydev_imps\_pydev_execfile.py", line 25, in execfile
    exec(compile(contents+"\n", file, 'exec'), glob, loc)
  File "C:\Users\DELL\git\process_grid\process_grid.py", line 949, in <module>
    options=slice_option)
  File "C:\home\miniconda\lib\site-packages\nco\nco.py", line 277, in get
    raise NCOException(**retvals)
nco.nco.NCOException: (returncode:3221225781) b'' 

The code where this is happening:

# assume the same longitude slice specs across temperature, precipitation, and soils files
slice_option = ['--dmn=lon,{0},{1},1'.format(precip_files[i][1], precip_files[i][2])]

# use NCO to slice the specified longitude range from the files
slice_file_precip = precip_files[i][0]
nco.ncks(input=args.precip_file, 
         output=slice_file_precip, 
         options=slice_option)

I can debug into the pynco code and see that this is happening in the nco.__getattr__.get() function, when it gets in there the cmd list object passed to the ncks binary looks like this:

<class 'list'>: ['C:/home/miniconda/pkgs/nco-4.7.1-vc14_0/Library/bin\\ncks', 
                 '--dmn=lon,0,20,1', 
                 '--output=C:/home/data/nclimgrid/work\\nclimgrid_lowres_prcp_slice00.nc', 
                 'C:/home/data/nclimgrid/nclimgrid_lowres_prcp.nc']

The error message appears to show an empty second input, b'', maybe this is being inserted by mistake somehow, as there is no second input file?

Where are things going wrong?

Answer 1

Your call to pyno appears correct. I am unable to recreate your error on a Linux box. And I don't have python on windows.

A couple of things you can try

1. Run the ncks command directly:

   C:/home/miniconda/pkgs/nco-4.7.1-vc14_0/Library/bin\ncks --dmn=lon,0,20,1 --output=C:/home/data/nclimgrid/work\nclimgrid_lowres_prcp_slice00.nc C:/home/data/nclimgrid/nclimgrid_lowres_prcp.nc

2. Try running the test modules in pynco/tests do this by running the command 'py.test' in your pynco directory. You may have to install the python module 'pytest'

...Henry