issues: 894125618

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id node_id number title user state locked assignee milestone comments created_at updated_at closed_at author_association active_lock_reason draft pull_request body reactions performed_via_github_app state_reason repo type
894125618 MDU6SXNzdWU4OTQxMjU2MTg= 5329 xarray 0.18.0 raises ValueError, not FileNotFoundError, when opening a non-existent file 9010180 open 0     8 2021-05-18T08:35:20Z 2022-09-21T18:19:57Z   NONE      

What happened:

In a Python environment with xarray 0.18.0 and python-netcdf4 installed, I called xarray.open_dataset("nonexistent"). (The file "nonexistent" does not exist.) xarray threw a ValueError: cannot guess the engine, try passing one explicitly.

What you expected to happen:

I expected a FileNotFoundError error to be thrown, as in xarray 0.17.0.

Minimal Complete Verifiable Example:

python import xarray as xr xr.open_dataset("nonexistent")

Anything else we need to know?:

This is presumably related to Issue #5295, but is not fixed by PR #5296: ValueError is also thrown with the currently latest commit in master (9165c266).

This change in behaviour produced a hard-to-diagnose bug deep in xcube, where we were catching the FileNotFound exception to deal gracefully with a missing file, but the new ValueError was of course not caught -- and the error message did not make the cause obvious. Catching ValueError is a workaround, but not a great solution since it may also be thrown for files which do exist but don't have a recognizable data format. I suspect that other codebases may be similarly affected.

xarray 0.17.0 was capable of throwing a ValueError for a non-existent file, but only in the (rare?) case that neither netCDF4-python nor scipy was installed.

Environment:

Output of <tt>xr.show_versions()</tt> INSTALLED VERSIONS ------------------ commit: None python: 3.9.4 | packaged by conda-forge | (default, May 10 2021, 22:13:33) [GCC 9.3.0] python-bits: 64 OS: Linux OS-release: 5.8.0-53-generic machine: x86_64 processor: x86_64 byteorder: little LC_ALL: None LANG: en_GB.UTF-8 LOCALE: en_GB.UTF-8 libhdf5: 1.10.6 libnetcdf: 4.8.0 xarray: 0.18.0 pandas: 1.2.4 numpy: 1.20.2 scipy: None netCDF4: 1.5.6 pydap: None h5netcdf: None h5py: None Nio: None zarr: None cftime: 1.4.1 nc_time_axis: None PseudoNetCDF: None rasterio: None cfgrib: None iris: None bottleneck: None dask: None distributed: None matplotlib: None cartopy: None seaborn: None numbagg: None pint: None setuptools: 49.6.0.post20210108 pip: 21.1.1 conda: None pytest: None IPython: None sphinx: None 
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