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  • xarray · 1 ✖
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
554376164 MDU6SXNzdWU1NTQzNzYxNjQ= 3718 losing shallowness of ds.copy() on ds from xr.open_dataset klindsay28 15570875 open 0     1 2020-01-23T20:02:55Z 2020-01-23T21:39:05Z   NONE      

MCVE Code Sample

``` import numpy as np import xarray as xr

xlen = 4 x = xr.DataArray(np.linspace(0.0, 1.0, xlen), dims=('x'))

varname = 'foo' xr.Dataset({varname: xr.DataArray(np.arange(xlen, dtype='float64'), dims=('x'), coords={'x': x})}).to_netcdf('ds.nc')

with xr.open_dataset('ds.nc') as ds: ds2 = ds.copy() ds2[varname][0] = 11.0 print(f'ds.equals = {ds.equals(ds2)}')

with xr.open_dataset('ds.nc') as ds: ds2 = ds.copy() print(f'ds.equals = {ds.equals(ds2)}') ds2[varname][0] = 11.0 print(f'ds.equals = {ds.equals(ds2)}') ```

Expected Output

I expect the code to write out ds.equals = True ds.equals = True ds.equals = True

However, when I run it, the last line is ds.equals = False

Problem Description

The code above writes a small xr.Dataset to a netCDF file. There are 2 context managers opening the netCDF file as ds. Both context manager blocks start by setting ds2 to a shallow copy of ds.

In the first context manager block, a value in ds2 is modified, and ds2 is compared to ds. The Datasets are still equal, confirming that the copy is shallow.

The second context manager block is the same as the first, except that ds2 is compared to ds prior changing the value the value in ds2. When this is done, the Datasets are no longer equal, indicating that ds2 is no longer a shallow copy of ds.

I don't understand how evaluating ds.equals(ds2), prior to changing a value in ds2, could decouple ds2 from ds.

I only observe this behavior when ds is set via xr.open_dataset. I don't see it when I create ds directly using xr.Dataset.

I'm rather perplexed by this.

Output of xr.show_versions()

INSTALLED VERSIONS ------------------ commit: None python: 3.7.6 | packaged by conda-forge | (default, Jan 7 2020, 22:33:48) [GCC 7.3.0] python-bits: 64 OS: Linux OS-release: 3.10.0-693.21.1.el7.x86_64 machine: x86_64 processor: x86_64 byteorder: little LC_ALL: en_US.UTF-8 LANG: en_US.UTF-8 LOCALE: en_US.UTF-8 libhdf5: 1.10.5 libnetcdf: 4.7.3 xarray: 0.14.1 pandas: 0.25.3 numpy: 1.17.5 scipy: 1.4.1 netCDF4: 1.5.3 pydap: None h5netcdf: None h5py: None Nio: None zarr: None cftime: 1.0.3.4 nc_time_axis: 1.2.0 PseudoNetCDF: None rasterio: None cfgrib: None iris: None bottleneck: 1.3.1 dask: 2.9.2 distributed: 2.9.3 matplotlib: 3.1.2 cartopy: None seaborn: None numbagg: None setuptools: 45.1.0.post20200119 pip: 19.3.1 conda: None pytest: 5.3.4 IPython: 7.11.1 sphinx: None 
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     xarray 13221727 issue

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