ValueError cannot guess the engine, try passing one explicitly with xarray 0.18

[weiji14]

Description of the problem

xarray v0.18 released on 6 May 2021 (see changelog at https://xarray.pydata.org/en/v0.18.0/whats-new.html) resulted in some API changes and this is breaking PyGMT tests that are trying to read from a *.grd file. Specifically the earth relief grids from the pygmt.datasets.load_earth_relief function don't work, and I think it also segfaults on Windows so it is a major issue.

For users: Temporary solution would be to downgrade to xarray v0.17.0 if you want to continue using the load_earth_relief function.

For PyGMT developers, we probably need to explicitly set an 'engine' in the xarray.open_dataarray() calls we make. Or we could post an upstream issue to xarray to handle *.grd files natively. Thoughts?

Full code that generated the error

PASTE CODE HERE

Full error message

https://github.com/GenericMappingTools/pygmt/runs/2523330164?check_suite_focus=true#step:11:1994

=================================== FAILURES ===================================
________________ [doctest] pygmt.accessors.GMTDataArrayAccessor ________________
011 
012     This is the GMT extension for :class:`xarray.DataArray`.
013 
014     You can access various GMT specific metadata about your grid as follows:
015 
016     >>> from pygmt.datasets import load_earth_relief
017     >>> # Use the global Earth relief grid with 1 degree spacing
018     >>> grid = load_earth_relief(resolution="01d")
UNEXPECTED EXCEPTION: ValueError('cannot guess the engine, try passing one explicitly')
Traceback (most recent call last):
  File "/usr/share/miniconda3/envs/pygmt/lib/python3.7/doctest.py", line 1337, in __run
    compileflags, 1), test.globs)
  File "<doctest pygmt.accessors.GMTDataArrayAccessor[1]>", line 1, in <module>
  File "/usr/share/miniconda3/envs/pygmt/lib/python3.7/site-packages/pygmt/helpers/decorators.py", line 438, in new_module
    return module_func(*args, **kwargs)
  File "/usr/share/miniconda3/envs/pygmt/lib/python3.7/site-packages/pygmt/datasets/earth_relief.py", line 136, in load_earth_relief
    with xr.open_dataarray(fname) as dataarray:
  File "/usr/share/miniconda3/envs/pygmt/lib/python3.7/site-packages/xarray/backends/api.py", line 673, in open_dataarray
    **kwargs,
  File "/usr/share/miniconda3/envs/pygmt/lib/python3.7/site-packages/xarray/backends/api.py", line 485, in open_dataset
    engine = plugins.guess_engine(filename_or_obj)
  File "/usr/share/miniconda3/envs/pygmt/lib/python3.7/site-packages/xarray/backends/plugins.py", line 112, in guess_engine
    raise ValueError("cannot guess the engine, try passing one explicitly")
ValueError: cannot guess the engine, try passing one explicitly
/usr/share/miniconda3/envs/pygmt/lib/python3.7/site-packages/pygmt/accessors.py:18: UnexpectedException
_____________ [doctest] pygmt.clib.conversion.dataarray_to_matrix ______________
040     ------
041     GMTInvalidInput
042         If the grid has more than two dimensions or variable grid spacing.
043 
044     Examples
045     --------
046 
047     >>> from pygmt.datasets import load_earth_relief
048     >>> # Use the global Earth relief grid with 1 degree spacing
049     >>> grid = load_earth_relief(resolution="01d")
UNEXPECTED EXCEPTION: ValueError('cannot guess the engine, try passing one explicitly')
Traceback (most recent call last):
  File "/usr/share/miniconda3/envs/pygmt/lib/python3.7/doctest.py", line 1337, in __run
    compileflags, 1), test.globs)
  File "<doctest pygmt.clib.conversion.dataarray_to_matrix[1]>", line 1, in <module>
  File "/usr/share/miniconda3/envs/pygmt/lib/python3.7/site-packages/pygmt/helpers/decorators.py", line 438, in new_module
    return module_func(*args, **kwargs)
  File "/usr/share/miniconda3/envs/pygmt/lib/python3.7/site-packages/pygmt/datasets/earth_relief.py", line 136, in load_earth_relief
    with xr.open_dataarray(fname) as dataarray:
  File "/usr/share/miniconda3/envs/pygmt/lib/python3.7/site-packages/xarray/backends/api.py", line 673, in open_dataarray
    **kwargs,
  File "/usr/share/miniconda3/envs/pygmt/lib/python3.7/site-packages/xarray/backends/api.py", line 485, in open_dataset
    engine = plugins.guess_engine(filename_or_obj)
  File "/usr/share/miniconda3/envs/pygmt/lib/python3.7/site-packages/xarray/backends/plugins.py", line 112, in guess_engine
    raise ValueError("cannot guess the engine, try passing one explicitly")
ValueError: cannot guess the engine, try passing one explicitly
/usr/share/miniconda3/envs/pygmt/lib/python3.7/site-packages/pygmt/clib/conversion.py:49: UnexpectedException
_____________________ [doctest] pygmt.clib.session.Session _____________________
095         If you try to call a method outside of a 'with' block.
096     GMTVersionError
097         If the minimum required version of GMT is not found.
098 
099     Examples
100     --------
101 
102     >>> from pygmt.datasets import load_earth_relief
103     >>> from pygmt.helpers import GMTTempFile
104     >>> grid = load_earth_relief()
UNEXPECTED EXCEPTION: ValueError('cannot guess the engine, try passing one explicitly')
Traceback (most recent call last):
  File "/usr/share/miniconda3/envs/pygmt/lib/python3.7/doctest.py", line 1337, in __run
    compileflags, 1), test.globs)
  File "<doctest pygmt.clib.session.Session[2]>", line 1, in <module>
  File "/usr/share/miniconda3/envs/pygmt/lib/python3.7/site-packages/pygmt/helpers/decorators.py", line 438, in new_module
    return module_func(*args, **kwargs)
  File "/usr/share/miniconda3/envs/pygmt/lib/python3.7/site-packages/pygmt/datasets/earth_relief.py", line 136, in load_earth_relief
    with xr.open_dataarray(fname) as dataarray:
  File "/usr/share/miniconda3/envs/pygmt/lib/python3.7/site-packages/xarray/backends/api.py", line 673, in open_dataarray
    **kwargs,
  File "/usr/share/miniconda3/envs/pygmt/lib/python3.7/site-packages/xarray/backends/api.py", line 485, in open_dataset
    engine = plugins.guess_engine(filename_or_obj)
  File "/usr/share/miniconda3/envs/pygmt/lib/python3.7/site-packages/xarray/backends/plugins.py", line 112, in guess_engine
    raise ValueError("cannot guess the engine, try passing one explicitly")
ValueError: cannot guess the engine, try passing one explicitly
/usr/share/miniconda3/envs/pygmt/lib/python3.7/site-packages/pygmt/clib/session.py:104: UnexpectedException
__________ [doctest] pygmt.clib.session.Session.virtualfile_from_grid __________
277         fname : str
278             The name of virtual file. Pass this as a file name argument to a
279             GMT module.
280 
281         Examples
282         --------
283 
284         >>> from pygmt.datasets import load_earth_relief
285         >>> from pygmt.helpers import GMTTempFile
286         >>> data = load_earth_relief(resolution="01d")
UNEXPECTED EXCEPTION: ValueError('cannot guess the engine, try passing one explicitly')
Traceback (most recent call last):
  File "/usr/share/miniconda3/envs/pygmt/lib/python3.7/doctest.py", line 1337, in __run
    compileflags, 1), test.globs)
  File "<doctest pygmt.clib.session.Session.virtualfile_from_grid[2]>", line 1, in <module>
  File "/usr/share/miniconda3/envs/pygmt/lib/python3.7/site-packages/pygmt/helpers/decorators.py", line 438, in new_module
    return module_func(*args, **kwargs)
  File "/usr/share/miniconda3/envs/pygmt/lib/python3.7/site-packages/pygmt/datasets/earth_relief.py", line 136, in load_earth_relief
    with xr.open_dataarray(fname) as dataarray:
  File "/usr/share/miniconda3/envs/pygmt/lib/python3.7/site-packages/xarray/backends/api.py", line 673, in open_dataarray
    **kwargs,
  File "/usr/share/miniconda3/envs/pygmt/lib/python3.7/site-packages/xarray/backends/api.py", line 485, in open_dataset
    engine = plugins.guess_engine(filename_or_obj)
  File "/usr/share/miniconda3/envs/pygmt/lib/python3.7/site-packages/xarray/backends/plugins.py", line 112, in guess_engine
    **kwargs,
/usr/share/miniconda3/envs/pygmt/lib/python3.7/site-packages/xarray/backends/api.py:485: in open_dataset
    engine = plugins.guess_engine(filename_or_obj)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

store_spec = '/home/runner/.gmt/server/earth/earth_relief/earth_relief_30m_g.grd'

    def guess_engine(store_spec):
        engines = list_engines()
    
        for engine, backend in engines.items():
            try:
                if backend.guess_can_open and backend.guess_can_open(store_spec):
                    return engine
            except Exception:
                warnings.warn(f"{engine!r} fails while guessing", RuntimeWarning)
    
>       raise ValueError("cannot guess the engine, try passing one explicitly")
E       ValueError: cannot guess the engine, try passing one explicitly

/usr/share/miniconda3/envs/pygmt/lib/python3.7/site-packages/xarray/backends/plugins.py:112: ValueError
_________________________________ test_grdinfo _________________________________

    def test_grdinfo():
        """
        Make sure grdinfo works as expected.
        """
>       grid = load_earth_relief(registration="gridline")

/usr/share/miniconda3/envs/pygmt/lib/python3.7/site-packages/pygmt/tests/test_grdinfo.py:15: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
/usr/share/miniconda3/envs/pygmt/lib/python3.7/site-packages/pygmt/helpers/decorators.py:438: in new_module
    return module_func(*args, **kwargs)
/usr/share/miniconda3/envs/pygmt/lib/python3.7/site-packages/pygmt/datasets/earth_relief.py:136: in load_earth_relief
    with xr.open_dataarray(fname) as dataarray:
/usr/share/miniconda3/envs/pygmt/lib/python3.7/site-packages/xarray/backends/api.py:673: in open_dataarray
    **kwargs,
/usr/share/miniconda3/envs/pygmt/lib/python3.7/site-packages/xarray/backends/api.py:485: in open_dataset
    engine = plugins.guess_engine(filename_or_obj)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

store_spec = '/home/runner/.gmt/server/earth/earth_relief/earth_relief_01d_g.grd'

    def guess_engine(store_spec):
        engines = list_engines()
    
        for engine, backend in engines.items():
            try:
                if backend.guess_can_open and backend.guess_can_open(store_spec):
                    return engine
            except Exception:
                warnings.warn(f"{engine!r} fails while guessing", RuntimeWarning)
    
>       raise ValueError("cannot guess the engine, try passing one explicitly")
E       ValueError: cannot guess the engine, try passing one explicitly

/usr/share/miniconda3/envs/pygmt/lib/python3.7/site-packages/xarray/backends/plugins.py:112: ValueError

System information

Please paste the output of python -c "import pygmt; pygmt.show_versions()":

PyGMT information:
  version: v0.3.2.dev131+gb51e3c2
System information:
  python: 3.9.2 | packaged by conda-forge | (default, Feb 21 2021, 05:02:46)  [GCC 9.3.0]
  executable: /usr/share/miniconda3/envs/pygmt/bin/python
  machine: Linux-5.4.0-1046-azure-x86_64-with-glibc2.31
Dependency information:
  numpy: 1.20.2
  pandas: 1.2.4
  xarray: 0.18.0
  netCDF4: 1.5.6
  packaging: 20.9
  ghostscript: 9.53.3
  gmt: 6.2.0rc1
GMT library information:
  binary dir: /usr/share/miniconda3/envs/pygmt/bin
  cores: 2
  grid layout: rows
  library path: /usr/share/miniconda3/envs/pygmt/lib/libgmt.so
  padding: 2
  plugin dir: /usr/share/miniconda3/envs/pygmt/lib/gmt/plugins
  share dir: /usr/share/miniconda3/envs/pygmt/share/gmt
  version: 6.2.0rc1