Disable the cfgrib backend if eccodes is not installed (#5083)

* Disable the cfgrib backend if eccodes is not installed

If cfgrib is installed, but libeccodes.so is not installed on the system, Xarray does not load as cfgrib will throw a RuntimeError(), which is not caught.

* Update xarray/backends/cfgrib_.py

Co-authored-by: Mathias Hauser <[email protected]>

* Update xarray/backends/cfgrib_.py

Co-authored-by: Mathias Hauser <[email protected]>

* Update cfgrib_.py

Missing import

* Run black

* Update whats-new.rst

* Update whats-new.rst

* Update xarray/backends/cfgrib_.py

Co-authored-by: Mathias Hauser <[email protected]>

Author: b8raoult

doc/whats-new.rst

@@ -61,6 +61,7 @@ New Features
   :py:class:`~core.groupby.DataArrayGroupBy`, inspired by pandas'
   :py:meth:`~pandas.core.groupby.GroupBy.get_group`.
   By `Deepak Cherian <https://github.com/dcherian>`_.
+- Disable the `cfgrib` backend if the `eccodes` library is not installed (:pull:`5083`). By `Baudouin Raoult <https://github.com/b8raoult>`_.
 
 Breaking changes
 ~~~~~~~~~~~~~~~~

xarray/backends/cfgrib_.py

@@ -1,4 +1,5 @@
 import os
+import warnings
 
 import numpy as np
 
@@ -20,7 +21,12 @@
     has_cfgrib = True
 except ModuleNotFoundError:
     has_cfgrib = False
-
+# cfgrib throws a RuntimeError if eccodes is not installed
+except RuntimeError:
+    warnings.warn(
+        "Failed to load cfgrib - most likely eccodes is missing. Try `import cfgrib` to get the error message"
+    )
+    has_cfgrib = False
 
 # FIXME: Add a dedicated lock, even if ecCodes is supposed to be thread-safe
 #   in most circumstances. See: